Aubrey de Grey - Ending Aging

E N D I N G AGING

E N D I N G A G I N G

The Rejuvena t ion

Break th roughs That

Could Reverse Human

Aging in Our Li fe t ime

A u b r e y d e G r e y , P h . D . ,

w i t h M i c h a e l R a e

S T . M A R T I N ' S P R E S S N E W Y O R K

ENDING AGING. Copyright © 2007 by Aubrey de Grey. All rights reserved. Printed in the

United States of America. No part of this book may be used or reproduced in any

manner whatsoever without written permission except in the case of brief quotations

embodied in critical articles or reviews. For information, address

St. Martin's Press, 175 Fifth Avenue, New York, N.Y. 10010.

www. stmartins.com

LIBRARY OF CONGRESS CATALOGING-IN-PUBLICATION DATA

De Grey, Aubrey D. N. J . , 1 9 6 3 -

Ending aging : the rejuvenation breakthroughs that could reverse human aging

in our lifetime / Aubrey de Grey ; with Michael Rae.—1st. ed.

p. cm.

ISBN-13: 978-0-312-36706-0

ISBN-10: 0-312-36706-6

1. Longevity. 2. Aging—Molecular aspects. 3. Biotechnology. I. Rae, Michael.

II. Title.

QP85.D348 2007

612.6'8—dc22

2007020217

First Edition: September 2007

1 0 9 8 7 6 5 4 3 2 1

Aubrey dedicates this book as follows: "To the tens of millions

whose indefinite escape from aging depends on our actions today."

Michael dedicates this book as follows: "To the two tenders of the

flames that have inspired me throughout this work. To April Smith,

for erupting, like Athena, out of the secret depths of my mind,

raining Greek fire on my Manichee heart, reigniting smoldering

embers I had thought long extinguished, and opening up the

promise of a shared indefinite tomorrow; and to Dr. Aubrey de

Grey, for tirelessly and courageously bearing Promethean fire to a

world yet shivering under the winter of age-related death and decay,

kindling the sparks that we must fan into a blaze that will cast out

its obscuring darkness and melt its frozen grip."

Contents

Preface ix

P a r t One 1

1. The Eureka Moment 3

2. Wake Up—Aging Kills! 7

3. Demystifying Aging 16

4. Engineering Rejuvenation 32

P a r t Two 47

5. Meltdown of the Cellular Power Plants 49

6. Getting Off the Grid 77

7. Upgrading the Biological Incinerators 101

8. Cutting Free of the Cellular Spider Webs 134

Viii C O N T E N T S

Notes

Glossary

Index

341

363

379

9. Breaking the Shackles of AGE 164

10. Putting the Zombies to Rest 200

11. New Cells for Old 238

12. Nuclear Mutations and the Total Defeat of Cancer 274

P a r t T h r e e 309

13. Getting from Here to There: The War on Aging 311

14. Bootstrapping Our Way to an Ageless Future 325

15. War Bonds for the Campaign Against Aging 335

Preface

The biomedical revolution described in this book is still some way

off—at least a few decades, maybe more. Why, you may then ask, should

you concern yourself with it now?

The answer is simple: Once you know what I have to tell you, you'll

want to make it happen sooner, and some of you will put that desire into ac-

tion. The more people are aware of what has now become foreseeable in

the fight against our oldest foe, aging, the faster it will become acceptable

to "come out" as an ardent opponent of aging, and then unacceptable not

to. We aren't close enough to this revolution to put accurate timescales on

its arrival, but we are close enough that our action (or inaction . . . ) today

will affect the date at which aging is defeated.

In fact, we've been at that point for a few years now. It could, therefore,

be argued that I should have written this book sooner. Well, maybe I should

have—but there's a trade-off: with every year that has passed since I devel

oped the key concepts described here, progress has been seen in the labora

tory. Every step of this progress has strengthened the case that the overall

scheme will succeed, so the book as a whole is more compelling than it

could have been a year or three ago. In fact, without the diligent efforts of a

X P R E F A C E

large number of scientists within and beyond biogerontology, my plan for

defeating aging could not exist.

Another reason this book has only been written now is the usual one:

books don't write themselves, and I've been spending every waking hour

engaged in other work to further the anti-aging mission. Without doubt,

you would not have this book in your hands today if it were not for the dili

gent work of my research assistant Michael Rae, who dedicated much of

2006 to it: he can take credit for most of the text of Part 2.

Michael is not the only person without whom this book could not have

come to pass. Thanks to Peter Ulrich for painstakingly going over the fasci

nating history of patient work, inspired reasoning, and scientific serendip

ity behind the development of alagebrium. Any misunderstandings of this

story are Michael's. Special thanks go to our graphics team, who prepared

the illustrations: Bram Thijssen, Bryan English, Benjamin Martin, Tyler

Chesley, Zachary Bos, Hoyt Smith, and their coordinator, Jeff Hall. Addi

tionally, Michael and I received outstanding editorial help from Methuselah

Foundation volunteers Reason, Anne Corwin, and David Fisher. Our

agent, John Brockman, and his staff were tremendously efficient in shep

herding the book through the worldwide publication process, and our edi

tor at St. Martin's, Phil Revzin, also provided invaluable editorial input.

And finally, my work on this book has, as with all my contributions to the

crusade against aging, depended hugely on the unswerving intellectual and

emotional support of my beloved wife, Adelaide Carpenter.

I hope that this book will enjoy a wide readership; if it does, most read

ers will be nonbiologists and certainly nonbiogerontologists. Some, how

ever, will be people who do possess expertise in these areas. To that group

I would like to make clear at the outset that, in presenting SENS, the

"Strategies for Engineered Negligible Senescence," to a general audience, I

have not been able to delve into every nook and cranny of the relevant sci

ence, and you will surely identify aspects of SENS that, if what you read

here were all there was to it, would seem flawed. I merely remind you now

that this book is not all there is to SENS, and that, if you see what seems to

you to be a slam-dunk objection to what I say, you should consult my pub

lished academic work (and, preferably, consult me personally, too) before

dismissing it.

However, the above applies only to "errors" of omission, of course. Any

errors of commission are, I fully accept, my responsibility and mine alone.

Part One

T h e E u r e k a M o m e n t

Marriott Hotel, Manhattan Beach, California.

June 25, 2000.

Four o'clock.

In the morning.

It was 4 A . M . in California, but my body insisted on reminding me

that it was noon in Cambridge. I was exhausted from the intercontinental

flight and by a day spent in debate with some of the most influential per

sonalities in biogerontology, at an invitation-only brainstorming workshop

on ideas to combat aging. Evolutionary biologist Michael Rose was there.

So were calorie restriction researchers Richard Weindruch and George Roth,

nanotechnologist Robert Freitas, and several others. But I couldn't sleep:

On top of the mismatch between biological and geographical clocks, I was

frustrated at what I saw as the day's failure to make any real progress to

ward a concrete, realistic anti-aging plan. As I dozed and pondered, a ques

tion on the nature of metabolism and aging wormed its way into my brain

and wouldn't let go.

In my bleary irritation, I sat up, ran my hands over my beard, and be

gan pacing the room, turning over the quandary in my mind. "Normal" me

tabolism was just so messy, and the raging debates in the biogerontology

literature showed how difficult it was to determine what paced what: which

metabolic disruptions were causes of aging, and which were effects (or sec

ondary causes) that would simply disappear if the underlying primary

causes were addressed. How could we make a positive difference in such a

complex, poorly understood system? How could any meaningful change

1

4 E N D I N G A G I N G

made in metabolism not be like a butterfly flapping its wings—apt to cause

large, unwanted storms further down the line?

Then a second line of thought began to form in my mind—idly at first,

just as a notion. The real issue, surely, was not which metabolic processes

cause aging damage in the body, but the damage itself. Forty-year-olds have

fewer healthy years to look forward to than twenty-year-olds because of dif

ferences in their molecular and cellular composition, not because of the

mechanisms that gave rise to those differences. How far could I narrow

down the field of candidate causes of aging by focusing on the molecular

damage itself?

Well, I thought, it can't hurt to make a list. . .

There are mutations in our chromosomes, of course, which cause can

cer. There is glycation, the warping of proteins by glucose. There are the

various kinds of junk that accumulate outside the cell ("extracellular aggre

gates"): beta-amyloid, the lesser-known transthyretin, and possibly other

substances of the same general sort. There is also the unwholesome goo

that builds up within the cell ("intracellular aggregates"), such as lipofus-

cin. There's cellular senescence, the "aging" of individual cells, which puts

them into a state of arrested growth and causes them to produce chemical

signals dangerous to their neighbors. And there's the depletion of the stem

cell pools essential to healing and maintenance of tissue.

And of course, there are mitochondrial mutations, which seem to dis

rupt cellular biochemistry by increasing oxidative stress. I had for a few

years felt optimistic that scientists could solve this problem by copying mi

tochondrial DNA from its vulnerable spot at "ground zero," within the

free-radical generating mitochondria, into the bomb shelter of the cell nu

cleus, where damage to DNA is vastly rarer.

Now, if only we had solutions like that for all of this other stuff, I mused,

we could forget about the "butterfly effect" of interfering with basic metabolic

processes, and just take the damage ITSELF out of the picture.

Hmm.

Well, I thought, why the bloody hell not?

I went back over my list. Protein glycation? A biotech startup was al

ready running clinical trials using a drug that had been shown to break the

dysfunctional handcuffing of the proteins that this process caused. The

extracellular aggregates? Here again, animal studies had shown that you

could just remove the damage, in this case by vaccinating against the amy

loid plaque and letting immune cells gobble the stuff up. In theory, at least,

there were all kinds of ways to deal with cellular senescence, though I wasn't

T H E E U R E K A M O M E N T 5

sure which of them would ultimately pan out. Anyone who'd read a news

paper in the last year knew that scientists were hotly pursuing a way to deal

with the loss of cells: stem cells, cultured in the lab and delivered as a reju

venating cellular therapy. Lipofuscin? It was at this point in my survey that I

began to feel I might really be on to something, because just a year previ

ously I'd come up with a way to eliminate lipofuscin that, although ex

tremely novel, had already secured the enthusiastic interest of a few of the

top researchers in that area. I didn't have any radical new ideas up my sleeve

for cancer; it was going to have to rely (for now, at least) on other people's

ideas. But that was okay: after all, there was already a huge effort under way

to deal with it. And as for other problems arising from nuclear mutations, I

had recently come to the admittedly counterintuitive conclusion that they

were not in fact a major cause of age-related cellular dysfunction.

I went over my list again and again, and as I did so I became ever surer

that there was no clear-cut exception. The combination of my own idea for

eliminating intracellular garbage like lipofuscin; the idea I'd been champi

oning for a few years for making mitochondrial mutations harmless; and the

various other therapies being worked on by others around the world for

addressing glycation, amyloid accumulation, cell loss, senescent cells and

cancer—it seemed that this was really and truly an adequately exhaustive list.

Not necessarily totally exhaustive—there certainly might be other things go

ing wrong in the body—but very possibly comprehensive enough to give a

few decades of extra life to people who are already in middle age before we

start the treatments. And that was certainly a much more promising first step

than anything that had been suggested the previous day, or in the many con

ferences and articles that I'd devoured over the previous few years.

For decades, my colleagues and I had been earnestly investigating ag

ing in the same way that historians might "investigate" World War I: as an

almost hopelessly complex historical tragedy about which everyone could

theorize and argue, but about which nothing could fundamentally be done.

Perhaps inhibited by the deeply ingrained belief that aging was "natural"

and "inevitable," biogerontologists had set themselves apart from the rest

of the biomedical community by allowing themselves to be overawed by the

complexity of the phenomenon that they were observing.

That night, I swept aside all that complexity, revealing a new simplicity

in a complete redefinition of the problem. To intervene in aging, I realized,

didn't require a complete understanding of all the myriad interacting pro

cesses that contribute to aging damage. To design therapies, all you have to

understand is aging damage itself: the molecular and cellular lesions that


impair the structure and function of the body's tissues. Once I realized that

simple truth, it became clear that we are far closer to real solutions to treat

ing aging as a biomedical problem, amenable to therapy and healing, than

it might otherwise seem.

Grabbing a notepad, I jotted down the molecular and cellular changes

that I could confidently list as important targets for the new class of anti-

aging therapies that I would soon call SENS, the "Strategies for Engineered

Negligible Senescence." Each of them accumulated with age in the body

throughout life and contributed to its pathological decay at later ages. As

far as I could tell, the list was exhaustive, but I'd present it to my colleagues

and see if they could add to it. I rushed downstairs before breakfast to tran

scribe my scrawled notes onto a flipchart in the meeting room. I was burst

ing to present my new synthesis to my esteemed colleagues. But truth be

told, I already knew full well that at this first hearing they'd greet it with

blank stares. The paradigm shift was just too great.

2

W a k e Up — A g i n g K i l l s

How many lives do you think you could save, in your life?

This is not a trick question. But in order to make it even more precise,

I'm going to modify it a little. When we speak of saving lives, we mean giv

ing the beneficiaries of our action the chance to live longer than they could

otherwise have lived. However, when we ask in detail about the importance

of saving a life, we may not regard all lives equally. For example, saving an

eighty-year-old from drowning may give him only a few extra years of life

before he's likely to die of something else, whereas saving a child from

drowning gives him a probable seventy years or more of extra life. We may

also take into account the quality of life of the persons whose lives we

save—predominantly their health. So here's my modified question:

How many healthy, youthful years in total do you think you

could add to people's lives, in your life?

The ultimate purpose of this book is to show you that you could add

many more years than you may currently think. So many, in fact, that now is

the time to decide whether you want to. The way you can do this is by help

ing to hasten the defeat of aging. The specifics of how you can help—by


donating money or time to the Methuselah Foundation's Mprize fund or its

SENS research funding program—will be the topic of Chapter 15; in this

chapter I'll restrict myself to communicating the magnitude of what those

efforts can achieve in humanitarian terms.

I'll start with some numbers. Around 150,000 people die each day

worldwide—that's nearly two per second—and of those, about two-thirds

die of aging. That's right: 100,000 people. That's about thirty World Trade

Centers, sixty Katrinas, every single day. In the industrialized world, the

proportion of deaths that are attributable to aging is around 90 percent—

yes, that means that for every person who dies of all causes other than aging

added together, be it homicide, road accidents, AIDS, whatever, some

where around ten people die of aging. 1

And it's worse than that. Look again at my expanded question and

you'll notice a couple of adjectives: "healthy" and "youthful." Many people,

when thinking about the idea of adding years to life, commit the "Tithonus

error"—the presumption that, when we talk about combating aging, we're

only talking about stretching out the grim years of debilitation and disease

with which most people's lives currently end. 2 In fact, the opposite is true:

the defeat of aging will entail the elimination of that period, by postponing

it to indefinitely greater ages so that people never reach it. There will, quite

simply, cease to be a portion of the population that is frail and infirm as a re

sult of their age. So it's not just extending lives that I'll be telling you about

in this book: it's the elimination of the almost incalculable amount of

suffering—experienced not only by the elderly themselves, of course, but by

their loved ones and carers—that aging currently visits upon us. Oh, and

there's the minor detail of the financial savings that the elimination of aging

would deliver to society: it's well established that the average person in the

industrialized world consumes more health-care resources in his or her last

year of life than in an entire life up to that point, irrespective of age at death,

so we're talking about trillions of dollars per year.

In this book I will explain the scientific and technological basis for my

view that we can probably eliminate aging as a cause of death this

century—and possibly within just a few decades, soon enough to benefit

most people currently alive. But first, I need to get you interested—not just

in the sense of entertainment, the sense in which you might read a good

story, but in the sense of realizing that as and when this becomes possible it

will be rather a good thing. And I've been in this business long enough to

know that a description of the level of suffering that would be averted and

the number of lives that would be saved does not, on its own, convince

W A K E U P — A G I N G K I L L S ! 9

most people that it would be a good thing if aging were defeated. So I hope

you'll forgive me if I am blunt and to the point in this chapter, before I

move on to the science and technology that will get the job done.

Why Did I Write This Book?

I'm a scientist and technologist, and in an ideal world I would spend essen

tially all my time working on the scientific and technological details of my

life's goal, defeating aging. I wouldn't spend much time doing media inter

views, or giving public lectures—or even writing books. But there's some

thing about people's attitudes to aging that, for now, changes my priorities.

I call it the pro-aging trance. I'm going to start my discussion of the pro-

aging trance with a comparison.

Here in the United Kingdom, just as across the whole Western world,

there is a campaign of increasing ferocity against smoking. All cigarette pack

ets come with health warnings. Not just tiny inconspicuous health warnings

in cautious scientific language, either—warnings of the most hard-hitting and

in-your-face nature possible. The simplest and shortest consists of just two

words, typically printed in black on a stark white background:

Smoking Kills

And, slowly but surely, smoking is becoming less popular. Just like

drunk driving before it, smoking is becoming socially disreputable. It's a

long, hard road, though: not just because nicotine is addictive, but because

youngsters continue to take up smoking despite the social stigma increas

ingly attached to it.

It's that latter point, the continued influx of new young addicts, that is

my focus here. I've used smoking as my chosen analogy not in order to con

demn the smokers among my readers—not at all. No, my focus here is

something altogether less controversial, because the battle to protect young

sters from taking up smoking is one that virtually all adults, smokers or not,

support. My reason for mentioning it here is timeliness: this battle is still be

ing waged, so we can examine at close quarters the contradictions in our at

titudes, both as individuals and as a society, that make the battle so hard to

win. With specific diseases, there is no argument: the more we can do to de

feat them, the better. But with smoking, even though it causes some of those

self-same diseases, somehow society is itself subject to an addiction that robs

1 0 E N D I N G A G I N G

it of its rationality concerning new young addicts. We face every day the bru

tal disconnect between allowing cigarettes to be advertised and sold widely

and seeing how much they blight and shorten the lives of those who fall un

der their spell. And it's just the same, I claim, with aging.

There are two potential reasons why smoking is declining in popularity

and in public acceptability. One is that many people find it unattractive—

they don't like the smell (or, in more intimate contexts, the taste). But it's

hard to believe that this can be the main trigger for the rather recent change

of sentiment against smoking, because today's tobacco is surely no more

off-putting than tobacco of a century or three ago. Thus, I think it's clear

that the main reason so many people now disapprove of smoking is its

other downside, which was not much appreciated even half a century ago:

It's really rather bad for you, and also for those around you. Most of all, it

massively increases your risk of getting fatal lung cancer, which not only

shortens your life but also makes your declining years really miserable.

My goal with this book, as for all my outreach work, is to inject mo

mentum into a similar shift of public opinion concerning aging. I have been

aware for many years that most people do not think about aging in the same

way that they think about cancer, or diabetes, or heart disease. They are

strongly in favor of the absolute elimination of such diseases as soon as pos

sible, but the idea of eliminating aging—maintaining truly youthful physi

cal and mental function indefinitely—evokes an avalanche of fears and

reservations. Yet, in the sense that matters most, aging is just like smoking:

It's really bad for you. It shortens your life (see Chapter 14 for an assess

ment of just how much), it typically makes the last several years of your life

rather grim, and it also makes those years pretty hard for your loved ones.

So let's look a little more closely at why aging is so passionately defended.

The Motivation for the Pro-Aging Trance

First of all, let me be clear that I realize there's an immense gulf between

people's attitude to modest postponement of aging and their attitude to the

topic of this book, the genuine elimination of aging as a cause of infirmity

and death. The anti-aging industry is huge, despite the (shall we say) highly

variable ability of its products to do what they say they can do, and that can

only be because people are not very happy to see themselves falling apart, or

to be seen to be falling apart. Yet, the prospect of eventually being able to

combat aging as well as we can currently combat most infectious diseases—

W A K E U P - A G I N G K I L L S ! 11

essentially to eliminate aging as a cause of death, in other words—strikes

terror into most people: Their immediate (and, I must point out, often high-

pitched) reaction is to raise the specter of uncontrollable overpopulation, or

of dictators living forever, or of only a wealthy elite benefiting, or any of a

dozen other concerns.

Now, I'm certainly not saying that these objections are dumb—not at

all. We should indeed be considering them as dangers that we should work

to preempt by appropriately careful forward planning. No: what shocks me

is not that these concerns are raised, but the way they're raised. People who

are totally rational and open to discourse on any other matter approach the

topic of defeating aging with a resistance to debate that virtually defies de

scription. The determination with which people work to change the sub

ject, to relegate the conversation to an exchange of witticisms, or simply to

cast the opponent of aging as a deluded nincompoop has to be encoun

tered to be believed.

Perhaps you're wondering whether I've forgotten that I'm talking

about you here. But understand that I'm not castigating you at all, because

my remarks so far have dealt only with the logic of why aging should be

fought, and life is not all about logic. There is a very simple reason why so

many people defend aging so strongly—a reason that is now invalid, but

until quite recently was entirely reasonable. Until recently, no one has had

any coherent idea how to defeat aging, so it has been effectively inevitable.

And when one is faced with a fate that is as ghastly as aging and about

which one can do absolutely nothing, either for oneself or even for others,

it makes perfect psychological sense to put it out of one's mind—to make

one's peace with it, you might say—rather than to spend one's miserably

short life preoccupied by it. The fact that, in order to sustain this state of

mind, one has to abandon all semblance of rationality on the subject—and,

inevitably, to engage in embarrassingly unreasonable conversational tactics

to shore up that irrationality—is a small price to pay.

A Word About SENS Skepticism

This book is a description of SENS (Strategies for Engineered Negligible

Senescence), my "project plan" for defeating aging. I expect that this will be

many readers' first encounter with SENS, but others will have come across

it before. In particular, if you have had an interest in life extension for some

time, there's a good chance that you've already come across accounts of


SENS in the mainstream media. If so, you'll be well aware that, while many

highly credentialed gerontologists have applauded SENS, others have

greeted it with strong criticism—even derision. So far in this chapter I have

only addressed the flaws in people's reasons for feeling that the defeat of ag

ing might not be desirable. But in order to ensure that you read this book

with real care, and moreover that you then go out and do something to help

the anti-aging effort, I also need to make sure that you understand that the

defeat of aging is feasible. Therefore, I include here a brief account of where

the debate about SENS's chances of success currently stands.

I must first make sure you appreciate that it is the norm for radical new

concepts that receive a lot of attention to arouse a sharp division of opinion

among expert commentators. In many cases, the establishment detractors

are absolutely right and the upstart new idea really is misguided. Very often,

however, the detractors have failed to acquire—even avoided acquiring—a

detailed understanding of what they are criticizing and have been driven

more by vested interests than by scientific argument. If you are not a scien

tist you may feel that this is an unfair suggestion, but the intellectual and

emotional investment that senior scientists have made in their beliefs is a

powerful opponent to objectivity: all scientists acknowledge this problem

privately, if not publicly. It has been memorably summarized by a number

of the world's most eminent scientists over the years; for example, the

physicist Max Planck observed over eighty years ago that "science advances

funeral by funeral," and the biologist J. B. S. Haldane noted that "there are

four stages of acceptance: (i) this is worthless nonsense; (ii) this is an inter

esting, but perverse point of view; (iii) this is true, but quite unimportant;

(iv) I always said so."

Since I work on aging in order to hasten its defeat, and not in order to

become rich and famous, I am extremely keen to identify any major holes

in SENS so that, if they indeed exist, I can go back to the drawing board

without delay. To this end, I talk to my most prominent biogerontologist

critics all the time about SENS. I am invariably driven to the view that they

are indeed guilty of reacting to my conclusion (that SENS can totally defeat

aging) without studying the reasoning behind that conclusion—but I of

course appreciate that I, too, may be unable to be objective in this matter.

For this reason, and also because the speed of implementation of SENS de

pends greatly on both public and academic acceptance that it might work,

I have worked hard in recent years to generate unbiased evidence as to

whether SENS is sense or nonsense. In 2006, I achieved this rather deci

sively, with the assistance of the prominent magazine MIT Technology Re-

W A K E U P - A G I N G K I L L S ! 13

view. After publishing a rather negative portrayal of SENS in 2005, TR dis

covered that the mainstream gerontologists on whose opinions it had relied

in choosing to do so were unwilling to back up their assessment with any

scientific detail. TR then admirably put itself at risk of considerable loss of

face by organizing a prize challenge to settle the matter.3

In order to win the SENS Challenge, one or a group of credentialed bi

ologists had to write a demolition of SENS that I was unable to rebut to the

satisfaction of a panel of expert judges. The panel of judges had to be

demonstrably impartial, of course, with no connection either to me or to

my critics, but yet well versed in biotechnology; TR succeeded in appoint

ing a superb five-person panel including the biotech luminary Craig Venter.

TR put up $10,000 as a prize, and the Methuselah Foundation contributed

the same amount. A group of nine highly credentialed biogerontologists

obligingly submitted a coauthored entry, as did two other scientists inde

pendently. All three entries were unanimously and emphatically judged to

fall decisively short of a demonstration that SENS is not worth trying.

Now, I'm certainly not trying to say that this proves that SENS will in

deed deliver the defeat of aging: there's only one way to answer that, which

is to implement it and see what happens. But my critics made the stronger

claim that SENS is so implausible that there's no need to try to implement

it. That claim has been incontrovertibly refuted by the SENS Challenge

process. So, if you find someone still eager to tell you that SENS is

fantasy—especially someone who claims to have expert knowledge in this

area—you'll know, as TR now knows, that asking such people what they

think about SENS is a great deal less reliable than asking them what they

know about SENS. And after you've read this book—especially Part 2—

you'll be equipped to come to your own conclusions.

<**P Building a Case, Chapter by Chapter

I'm a fighter at heart; I would never have made my peace with aging, how

ever lost the battle seemed. But that's not the life everyone wants, and I re

spect that. Thus, I would probably not have written this book if I thought

we were still too far from defeating aging to have any real chance of success

within the lifetimes of anyone alive today. In the next chapter I'll describe

why aging is, in principle, just as amenable to modulation and eventual elim

ination as specific diseases are, and how an inappropriate way of looking at

aging has led most gerontologists to favor eventual therapeutic approaches


that I consider unlikely to bear fruit. Then, Chapter 4 provides an overview

of my scheme for defeating aging within (if all goes well) only a few decades.

That concludes Part 1 of the book. In Part 2, Chapters 5 through 12 elabo

rate on the individual components of that scheme. The book concludes with

Part 3, a trio of chapters covering what I predict will be the response of so

ciety to initial successes in the laboratory a decade or so from now, how the

advances of the next few decades will be progressively refined and aging

permanently kept at bay, and how you can already help to accelerate that

crusade.

Buried inconspicuously in that last paragraph was something that I

want to make sure you don't misinterpret: a tentative time frame. Yes, I

consider that if funding is sufficient we have a 50/50 chance of developing

technology within about twenty-five to thirty years from now that will, un

der reasonable assumptions about the rate of subsequent improvements in

that technology, allow us to stop people dying of aging at any age—

equivalent to the effect of today's antiretrovirals against HIV. There are

three big caveats in that statement, though. The first is that it's only a 50

percent chance. Any technological prediction as far in the future as twenty-

five to thirty years is necessarily very speculative, and if you ask me how

soon I think we have a 90 percent chance of defeating aging I wouldn't

even be willing to bet on one hundred years. But I think a 50 percent

chance is well worth shooting for—don't you? The second caveat is that ag

ing won't be totally defeated by the initial versions of this technology; we'll

have to carry on improving it at a reasonable rate in order to keep aging

permanently at bay. I will explain all the details of that in Chapter 14.

But the third caveat is perhaps the most important: the adequacy of re

search funding. I cofounded the Methuselah Foundation in order to ad

dress that problem: at present, the pace of most of the research avenues

that we need to pursue in order to combat aging adequately is limited by

funding. If you can help to change that—whether by giving money your

self, or by influencing friends, or by writing or broadcasting on the

subject—you'll be making as much difference to the speed with which ag

ing is overcome as if you were doing the science yourself.

There's a critical point about funding that I must emphasize here: the

pivotal role of relatively small amounts of money at this early stage in the

crusade. I've complained at length in this chapter about people's reluctance

to treat aging as the curse that it is, and I hope I'm making a difference to

that attitude by my outreach activities, but realistically I know that most

people are going to sustain their pro-aging trance for a while yet, and that

W A K E U P — A G I N G K I L L S ! 15

will severely limit the availability of either public or commercial funding for

life extension research. The point where that will really change—where the

global pro-aging trance will collapse like a house of cards—will, in my view,

be when middle-aged mice are rejuvenated thoroughly enough to extend

their healthy lives by a large amount. This is a milestone that I've termed

"robust mouse rejuvenation," or RMR. The amount of money needed to

achieve it is tiny compared to how much we'll then need to spend to get the

same result in humans; but when humanity as a whole is behind the effort,

willing to pay for it with taxation, there'll be ample funds available. It's

now, when private philanthropy is the only major source of funding for

such work, that the magnitude of that private philanthropy is so critical. I'll

elaborate on this in Chapter 13.

I've discussed in this chapter why aging is defended, but I haven't said

much about how—about the common objections to the prospect of indefi

nite life extension. In many of my writings and public presentations, and on

my Web site, 4 I do address the many questions that arise concerning how

society would be different in a post-aging world, and especially how we

would handle the transition to that world. This book does not address

those issues in detail; I've decided to deal here only with the practicality of

radical life extension. I hope you'll come away with a pretty good under

standing that the genuine defeat of aging is a feasible goal. Whether it's also

a desirable goal is a question that you'll then be able to consider more

seriously—even, dare I say it, more responsibly and conscientiously—than

you could if you still thought it was science fiction.

3

D e m y s t i f y i n g A g i n g

Aging has held us in a psychological stranglehold ever since we

realized it existed, and that stranglehold remains intact to this day. I dis

cussed in Chapter 2 the effect that this has on our willingness to think ra

tionally about how terrible a thing aging is, and I explained why this

irrationality used to have a valid psychological basis while there was no hope

of combating aging, and also why it is now such a formidable obstacle.

There's a complication, though. I've told you that we've recently reached

the point where we can engage in the rational design of therapies to defeat

aging; most of the rest of this book is an account of my favored approach to

that design. But in order to ensure that you can read that account with an

open mind, I need to dispose beforehand of a particularly insidious aspect

of the pro-aging trance: the fact that most people already know, in their

heart of hearts, that there is a possibility that aging will eventually be de

feated.

Why is this a problem? Indeed, at first sight you might think that it

would make my job easier, since surely it means that the pro-aging trance is

not particularly deep. Unfortunately, however, self-sustained delusions don't

work like that. Just as it's rational to be irrational about the desirability of ag

ing in order to make your peace with it, it's also rational to be irrational about

D E M Y S T I F Y I N G A G I N G 1 7

the feasibility of defeating aging while the chance of defeating it any time

soon remains low. If you think there's even a 1 percent chance of defeating

aging within your lifetime (or within the lifetime of someone you love), that

sliver of hope will prey on your mind and keep your pro-aging trance un

comfortably fragile, however hard you've worked to convince yourself that

aging is actually not such a bad thing after all. If you're completely convinced

that aging is immutable, by contrast, you can sleep more soundly.

The key qualification in what I've just said, of course, is the phrase

"while the chance of defeating it any time soon remains low." Once that

chance becomes respectable, you're better off doing your bit to increase it

further—not just the actual laboratory work, of course, but also agitating,

cajoling, helping others (not least those with influence over research fund

ing) to awaken from their own pro-aging trance. Conversely, if the chance

of aging being defeated is really tiny despite whatever you do, the cost-

benefit balance of abandoning your comfort zone may tip the other way, in

favor of applying the same irrationality to the existence of such a possibility

as you may be doing in respect of the pros and cons of aging.

Therefore, in this chapter I'm going to describe what aging is in practi

cal terms, so as to demystify it for you. By doing so I plan to show you that

the popular presumption that aging is a phenomenon unlike all other

health conditions, somehow beyond even the theoretical reach of medical

technology, cannot be reconciled with established fact. Thus, by the end of

this chapter I aim to have placed you in the awkward position of still want

ing to believe (for your own peace of mind) that aging is immutable and

thus not worth worrying about, but no longer actually being able to believe

that. From that point on, my task will be the relatively easy one of explain

ing why our chances of defeating aging in the foreseeable future are not just

non-zero, but high enough to justify my having broken your pro-aging

trance in the first place. Justify, because once your pro-aging trance is no

more, you—yes, you—can make a difference to how soon aging is defeated,

and the fulfilment you will derive from that effort will far outweigh any

comfort you may have found in your previous certainty that aging can never

be combated.

The Illusory Boundary Between Aging and Disease

It used to be the case that people died of aging, but, if you believe what's

written on death certificates, these days they rarely do. The phrase "natural


causes" was the accepted term for the cause of death when it occurred at an

advanced age and in the absence of clearly defined pathology. These days,

however, that's considered inadequately informative, and coroners or their

equivalent are encouraged to enter something more specific.1

We all know, however, that quite a few people do indeed die in that

way—not from a heart attack, not from pneumonia or influenza, not from

cancer, not even from a stroke, but just peacefully, often in their sleep, be

cause their heart simply stops. These relatively lucky people indisputably

die of aging.

That brings me to the first of several times in this book when I must en

gage in the unpleasant business of exposing a serious distortion of the facts

that has been perpetrated—often unintentionally, I realize—by a large

number of senior researchers in the field of biogerontology, the study of

how aging works. This distortion has by now been generally seen for the

awful error that it was, but the disastrous consequences for the field are still

being felt, and probably will be for many years to come. Through the

1950s, '60s, and 70s , while gerontology was making its big push for recog

nition as a legitimate biological discipline, rhetoric developed to the effect

that the infirmities of aging should be viewed as separable into two distinct

phenomena: on the one hand, age-related diseases, and on the other hand,

"aging itself." This distinction was publicly defended mainly on the basis

that everyone has aging, whereas no age-related disease is universal. The

motivation for this distinction, on the other hand, was purely pragmatic: by

ring-fencing their area of work intellectually, gerontologists hoped to ring-

fence it financially, too.

And ring-fence it they did, most notably with the creation (while Pres

ident Richard Nixon was paying limited attention, so it is said) of the Na

tional Institute on Aging. 2 So far, so good. However, it's not good enough.

All gerontologists know full well that it's no accident that age-related dis

eases are age-related: they appear at advanced ages because they are conse

quences of aging, or (to put it another way) because aging is no more and

no less than the collective early stages of the various age-related diseases.

Gerontologists knew this back then, too. Thus, they also should have seen

back then that, by trumpeting the short-termist rhetoric that "aging is not a

disease," they were constructing an immense obstacle for themselves in the

longer term: the response from policy makers that, well, if it's not a disease,

why should we spend money on combating it? The era of that backlash be

gan decades ago and shows no sign of ending. Gerontologists these days

point out over and over again that if we could just postpone aging even a


little bit we would derive far more health benefits than would result from

even the most decisive breakthroughs against specific diseases, but over

and over again their paymasters fail to get the message. 3 I maintain that it is

overwhelmingly the inaccurate rhetoric of gerontologists, resulting from

their misguided policy of previous decades, that has brought about such

entrenched resistance to a simple, obvious and (within the field) universally

agreed-upon truth about the potential value of postponing aging.

I told you just now that age-related diseases are merely consequences

of aging; now I'll tell you why we know that. In the process, I'll also tell you

why aging has the range of speeds that it does—within a single individual,

and between individuals, and also between species.

Why Aging Doesn' t Need a Timer

The fact that a fair proportion of people die of natural causes, rather than

of any specific disease, might at first sight imply that aging is a process inde

pendent of diseases: something that increases people's vulnerability to dis

ease (thus making diseases more common among the elderly) but that also

kills us itself if no disease does so first. This is only partly correct. The el

derly are indeed more vulnerable to infectious diseases, because one aspect

of aging is the decline of the immune system. However, most diseases of old

age have only a minor, if any, infectious component: they are mostly or

wholly intrinsic. Take cancer, for example. A few types of cancer affect

young people, but most types are never seen in people below the age of

forty or so (except for people with very rare congenital DNA repair defi

ciencies). Some cancers are caused by viral infections—the best known of

these is cervical cancer, caused by the human papilloma virus. But the ma

jor underlying cause of cancer is the simple accumulation over time of mu

tations in our chromosomes. Mutations are inevitable: they happen as a

purely intrinsic side effect of our biology. The time they most often happen

is when the DNA of our chromosomes is replicated during the process of

cell division. The accumulation of mutations is, therefore, part of aging,

and cancer is predominantly a consequence of aging—or, if you prefer, part

of the later stages of aging.

Sounds pretty simple, doesn't it? And yet, there is a pervasive

presumption—one shared even by some biologists—that aging is some kind

of mysterious phenomenon qualitatively different from any disease: some

thing that has eluded, and thus may forever elude, biological elucidation.


There are a few main reasons for this presumption, so I'll briefly describe

those reasons and why they're wrong.

The first is that aging proceeds so much more slowly than specific dis

eases. So slowly, in fact, that we hardly notice its progression, whereas we

are much more keenly aware of the more rapid development of conditions

like cancer or diabetes. This is a conspicuous difference, but in fact it's just

what one would expect, because aging is a downward spiral. The more we

age, the more our self-repair functions decline, so the less able our body is

to stop us aging, so we age faster and faster. So it's to be expected that the

late stages of aging, the diseases, would go faster than the earlier stages.

Another thing that confuses people about aging is that it proceeds at

very different rates in different species but at pretty similar rates in all

members of a given species. This might be thought to imply that there is

some kind of internal clock driving the process, which is set at different

speeds in different species. The inference is that this clock is somehow im

mune to biomedical intervention, because changing its speed would re

quire us to stop being human. But that's not correct either, for two reasons.

First, even if there were such a timer, we could in principle postpone the

later stages of aging without changing the speed of the timer itself—I'll be

elaborating on this below. And second, if there were such a clock, why

shouldn't it be amenable to biomedical intervention anyway? The fact that

organisms of the same species tend to age at the same rate is just one conse

quence of the fact that they're genetically very similar to each other. It says

nothing about what can or cannot be altered by biomedical technology.

Perhaps the most common reason for the belief that there is an "aging

clock" is the fact that the various outcomes of aging (including age-related

diseases) all tend to appear at more or less the same age in different indi

viduals within a given species. Surely this must mean that there is indeed a

central aging clock, which has ticked down enough to set these diseases on

their way, right? No—and, again, this is for two main reasons.

First, this is exactly what one would expect if the debilities of old age

were just the later stages of a multifaceted decay process, just so long as that

system has one key feature: a rich degree of interconnection of the various

chains of cause and effect. If lots of things are going quietly wrong through

out life, and their accumulation is feeding back on themselves and each

other to accelerate them, they'll necessarily all proceed at more or less the

same rate and all "go critical" (explode into clinically identifiable disease)

at about the same age. And that interconnectedness is, indisputably, indeed

present in aging.

D E M Y S T I F Y I N G A G I N G 21

Second, if we think about the evolutionary basis of aging for a moment

we can easily see that, even without much interconnection between the

chains of events that lead to the various diseases of aging, we'd still expect

to have them all emerge at roughly the same age. This is because, if we had

genes that defended against one particular cause of death so well that

everyone was dead from other causes before they died of that one, those

genes would not be protected by evolutionary selection and would accu

mulate random, mild mutations from one generation to the next. Over evo

lutionary time, therefore, the quality of those genes would thereby sink

down to the point where the disease they protected against occurred at the

same age as all other age-related diseases.

Another common but incorrect reason for thinking that aging is some

how special is that it is "universal"—it happens to everyone. Well, yes: If

you live long enough, you'll exhibit signs of aging. But this is only a corol

lary of my earlier point about rates—that aging is really slow compared to

age-related disease. Because age-related diseases progress from diagnos-

ability to death rather quickly, many people die of one such disease before

the others emerge, or at least while they are still too early-stage to have been

diagnosed. But if those people hadn't suffered the disease that killed them,

they'd have lived long enough to suffer others. In fact, all the diseases of ag

ing are universal in the sense in which the question ought to be asked:

namely, you'll definitely get them if you don't get something else first.

Thus, in concluding this section I hope to have convinced you that ag

ing is not something inherently mysterious, beyond our power to fathom.

There is no ticking time bomb—just the accumulation of damage. Aging of

the body, just like aging of a car or a house, is merely a maintenance prob

lem. And of course, we have hundred-year-old cars and (in Europe any

way!) thousand-year-old buildings still functioning as well as when they

were built—despite the fact that they were not designed to last even a frac

tion of that length of time. At the very least, the precedent of cars and

houses gives cause for cautious optimism that aging can be postponed in

definitely by sufficiently thorough and frequent maintenance.

The Corollary That Even Most Experts Overlook

Everything I've explained above is well known to biogerontologists, the

people who study aging. From the way that most biogerontologists go about

exploring how to postpone aging, however, you might think they didn't


know this at all. People who work to combat specific diseases explore the way

in which the disease progresses and look for ways to disrupt that pathway. In

gerontology, however, the predominant modus operandi for designing inter

ventions is to compare organisms that age at different rates—different

species, or individuals of the same species in different conditions—and to

come up with ways to copy or extrapolate those differences so as to make ag

ing happen more slowly. This is effectively an a priori capitulation, not even

trying to dissect and disrupt the process but rather treating it as a black box.

It's especially surprising when you bear in mind that biogerontologists cer

tainly do work hard to dissect the aging process in order to understand it—

just not in order to combat it. (Unfortunately, these two goals motivate

different types of dissection.) Rather, the most promising ways to postpone

aging are by disrupting the pathways underlying it, just as we do for specific

diseases. Thus, since aging is just the accumulation of damage, we should be

looking at ways to alleviate that accumulation. I'll return to this in greater de

tail in the next chapter and beyond.

Why Fixing Aging Is Easier than Fixing Similarly

Complex Machines

Now let's move on to another reason that people often give for clinging to

the belief that aging is inherently inaccessible to biomedical intervention. If

aging is just damage, and the body is just a complex machine, it stands to

reason that we can apply the same principles to alleviating the damage of

aging as we do to alleviating damage to machines. But people sometimes

point out that the body has a host of self-repair and self-maintenance pro

cesses, which machines basically don't have, hence we're not really ma

chines at all. Thus, they claim, the maintainability of machines is no basis

for confidence that the body is in principle similarly maintainable.

Well, I invite you to think about that logic for a moment. We have

built-in repair and maintenance machinery. Why on earth would that make

it harder to maintain our bodies in good working order? Clearly the oppo

site is the case: if our bodies are doing most of the job automatically, that

leaves less for us to do with biomedical technology.

Let me stress that I'm not saying the task is easy. The body is a great deal

more complicated than any man-made machine—and what's more, we didn't

design it, so we have to reverse-engineer its workings in order to understand

it well enough to keep it running. But that doesn't change the above logic: the


natural capacity for self-repair that we're born with is our ally in the anti-

aging crusade, not our enemy.

Postponed Aging in the Lab: No Longer Just Theory

By now I may have satisfied some readers that, indeed, aging is not a mysti

cal phenomenon beyond the reach of mere, um, mortals. I'm well aware,

however, that many people find theoretical arguments only modestly per

suasive, even if no holes in those arguments seem evident. Such people—

you, perhaps—feel altogether more comfortable with a conclusion if it is

backed up by hard evidence. You'll be pleased to discover, then, that for

several decades scientists have been finding ways to lengthen the lives of

various organisms in the laboratory. Best of all, they've done this not by ex

tending those organisms' period of declining vigor at the end of life, nor (by

and large) by keeping them immature for longer, but by extending the pe

riod of peak health and vigor between maturity and frailty.

One highly robust life-extension technique was discovered over twenty

years ago by a young Canadian researcher named Michael Rose, who is

now a professor at the University of California, Irvine. Rose is an evolution

ary biologist, and at that time he already had a thorough knowledge of the

ways in which evolution optimizes a species' longevity for its ecological

niche. He realized that it might be possible to breed longer lived organisms,

rather in the vein of the Howard families in Robert Heinlein's Lazarus Long

books, by maintaining them over many generations and only allowing those

with the longest lives (actually, strictly speaking the longest reproductive

lives) to contribute to the next generation. It would take many more gener

ations than Heinlein described, but Rose was working with fruit flies,

which reach maturity only a week after their own conception. And it

worked, spectacularly: Rose was eventually able to achieve average lifes

pans twice those in his starting population. 4

This approach, impressive though it was, has a fundamental and rather

relevant limitation—a limitation that has probably not escaped you. Specif

ically: it can't be applied to you, only to your great-great-great. . . great

grandchildren. Rose knew this, too, of course, and more recently he's been

working hard to identify the genetic, and thence molecular, basis for this

life extension with a view to eventual therapies that might work on those of

us unfortunate enough to be already alive. But thus far, all he has are long-

lived distant descendents of short-lived flies.


Luckily, other laboratory life-extension successes have not shared this

drawback. The first and best-known way to delay aging in the laboratory

was discovered way back in the 1930s by a researcher named Clive McCay,

working with laboratory mice. 5 It is called calorie restriction—or some

times dietary restriction, energy restriction or food restriction. It's an ex

traordinarily simple concept: If you feed rodents (or, in fact, a wide variety

of other animals) a bit less than they would like, they tend to live longer

than if they have as much food as they want. This is not simply because

such animals tend to overeat given the chance and become obese: animals

that "eat sensibly" and maintain a constant body weight throughout most

of their lives still live less long than those given less food.

The next researcher (not counting Rose) to take the postponement of

aging a major leap forward was a geneticist working with a third, almost

equally widely studied, model organism: the nematode worm Caenorhabdi-

tis elegans. His name is Tom Johnson. He was not, strictly speaking, the dis

coverer of the phenomenon I will describe here—that honor goes to one of

his coworkers—but he spearheaded the work on it for some years and that

work has become identified with him, so I'll focus on him for the moment.

What Johnson and his colleagues discovered and researched was a muta

tion in a single, identified gene, which on its own—without any of the sus

tained selective pressure employed by Rose—added at least 50 percent to the

youthful adult lifespan of his worms. 6 This was an immense breakthrough,

because single genes can be modified in the test tube and then introduced

into the body by gene therapy: either germline gene therapy, which affects

only the recipient's descendents, or somatic gene therapy, which affects the

organism that receives the treatment. Somatic gene therapy for humans is

still taking its baby steps, but there is widespread confidence that it'll work

well eventually. And human germline gene therapy raises ethical concerns

(though there are technical approaches to avoiding these). But as a proof of

principle, the postponement of aging by a single, defined genetic alteration

is vastly closer to clinical applicability than something accomplished by se

lection over many generations and affecting an unknown number of genes.

Perhaps because of this, and also partly because of the experimental

methods involved, Johnson's result initiated a massive surge in attempts to

identify genetic alterations to lab animals that would delay their aging. This

surge actually took a few years to get going, but when a second laboratory

(that of Cynthia Kenyon at the University of California San Francisco)

identified a mutation in a different gene, also in nematodes, that extended

their lives even more than Johnson's mutation did, the topic became one of


the hottest in the whole of biology.7 Kenyon and other top biogerontology

researchers have been able to publish nearly all their best work in the very

top few journals ever since—journals that scientists in most fields are lucky

to publish in even a couple of times in their whole career.

Johnson's and Kenyon's mutations were in different genes, but these

genes participate in largely the same range of metabolic processes. In partic

ular, they help to mediate an alternative developmental trajectory that nor

mal, nonmutant nematodes can follow, termed the dauer pathway. When a

nematode larva follows the dauer pathway, it suspends its development for a

period than can last much longer than the entire lifetime of a nematode that

follows the normal, non-dauer trajectory. What, you may ask, triggers this

developmental choice? And what "restarts" development and the resump

tion of the path toward normal nematode adulthood? Well, it just so hap

pens that the usual trigger for entry into the dauer pathway is starvation, and

that exit from dauer is stimulated by the presence of food. In other words,

the dauer pathway is neither more nor less than nematodes' extreme version

of rodents' response to calorie restriction.

Since Johnson's and Kenyon's breakthroughs, many other mutants

have been discovered—not only in nematodes but also in fruit flies and

mice—that have extended lifespans, and nearly all of these mutations have

also disrupted genetic machinery that mediates the sensing or metabolism

of nutrients. In general, the mutations confer a delay of aging at most equal

to that achievable by simply restricting calorie intake. 8 A few publications

have appeared in the past few years reporting life extension in mice caused

by reducing oxidative stress,9,10,11 but I am currently cautious about the re

producibility of these findings, because a huge number of other attempts to

postpone mouse aging in the laboratory in that way has failed.

At this point, therefore, I can point to a pretty compelling, double-

whammy argument that aging is worth trying to tackle. On the one hand we

should in principle be able to postpone aging by a large degree; moreover,

we have actually done so in the laboratory. This is surely great cause for op

timism that we will do so in the clinic in the not-too-distant future.

Isn't it?

Well, I would hardly have written this book if that were not indeed my

ultimate conclusion. However, the operative word here is "ultimate." Be

fore closing this chapter, I must explain why calorie restriction and its gene

tic emulation are not, in fact, pointers to the most promising route to

combating human aging.


Calorie Restriction and Its Emulation: A False Dawn

Do you know any perfectionists?

I do—and I always have, because my mother is one. I certainly

wouldn't be where I am today without my mother, and that includes her in

fluence on me as well as her sheer hard work and determination to give me

the best start in life. But there are certain ways in which her influence on

me was to show me a bad example, and her perfectionism is perhaps the

most extreme such case. I feel that in many ways it has prevented her from

achieving what she might have in her life, so I've never let myself become a

perfectionist—and I've certainly never regretted that.

What's wrong with perfectionism? We all know the main problem with

it: Perfectionism takes time. Most people are interested in getting things

done, and there are many circumstances in which a quick and dirty job is

the best policy, because the advantages of the "quick" outweigh the disad

vantages of the "dirty." There are certainly other circumstances in which

the balance is reversed, though—where a more painstaking approach is to

be preferred; hence, the ideal is to have good intuition and judgment for

how much attention to detail is appropriate in any particular case.

You may think that the above two paragraphs are a remarkably dra

matic digression, so let me surprise you by bringing my chain of reasoning

straight back to calorie restriction and its limitations in just a single sen

tence. The life-extending response to nutrient deprivation is neither more

nor less than the expression of an organism's genetically programmed intu

ition regarding the appropriate degree of attention to detail that it should

exercise with regard to its day-to-day molecular and cellular functioning—

and, because that's all it is, it's not amenable to substantial enhancement by

foreseeable biomedical technology.

Some elaboration is in order, so here goes.

I've explained, earlier in this chapter, that there are no genes for aging

in most species, simply because genes only survive if they confer enough

benefit (and thereby enjoy enough selective pressure for their survival) to

outweigh the constant stream of random mutations that all genes experi

ence over evolutionary time, and a gene can't confer any benefit if it only

mediates a process that would happen anyway. The only species in which

aging is actively driven by genetic machinery are those (such as salmon) in

which there is some reason to age and die rapidly—something that does not

happen by default to a machine that was running well for a long time


previously. Slow aging, the sort that we see in nearly all species, is the de

fault scenario, so no genes causing it can survive.

What we most certainly do have genes for, by contrast, is the panoply

of interacting processes that turns each of us from a single cell into a fertile

adult and that maintain our vigor and fertility until an age at which (in the

wild) we're very likely to have succumbed to starvation, predation, and so

on. Now, what does that have to do with perfectionism? Well, the reason

we have genes to keep us going until we're very likely to have been killed is

because the longer our fertile lives continue, the more progeny we'll have

time to have, so the greater the chance that our genes will be passed to fu

ture generations.

But what about the other end of our fertile life—the beginning? The

same applies: the sooner we achieve sexual maturity, the more offspring

we'll have time to produce before we die. But here's the problem: the be

ginning and end of fertile life are not independent of each other. Growth

from a single cell to a fertile adult is a process as complex as any known,

and mistakes always happen during its execution. You can probably see the

light at the end of this logical tunnel now: The organism has a choice be

tween doing a quick and dirty job of its growth, leading to early fertility but

sloppy construction, or a more perfectionist job that delays sexual maturity

but creates a more smooth-running machine in the end. And a more slop

pily constructed animal will on average live less long—partly because it

may be less able to defend itself against predators, famine, and such like,

but also because the molecular and cellular damage that it laid down dur

ing its headlong rush to maturity has effectively given it a head start in the

aging process. There's abundant evidence that this is not just a reasonable

idea but is also actually borne out in nature: for example, when you com

pare different species that are same size, the one that matures later tends to

be the longer-lived.

So now: What does this have to do with calorie restriction, dauers,

and the related genetic manipulations that I surveyed earlier in this chap

ter? Well, it's actually very simple. In a famine, there are two big problems

with passing on your genes. Firstly, gestation consumes a lot of energy,

which of course comes from food. And secondly, whatever offspring you

do succeed in having during a famine are very likely to die of starvation

before they can have their own offspring, which is no better for the sur

vival of your genes than if you hadn't had any offspring in the first place.

Thus, the advantage (in terms of your genetic heritage) of maturing


quickly is less during a famine than when food is plentiful. But wait: the

disadvantage of maturing quickly, namely the increased risk of death that

results from being sloppily constructed, is unaltered! In fact, that risk may

in some cases be amplified: If the duration of a particular famine is a large

fraction of the species's lifespan, the period late in life when the well-

constructed, late-aging animals are the only ones left to procreate will be

the only period when successful procreation can occur. In that case, the

benefit of being well constructed (i.e., the drawbacks of being sloppily

constructed) will be greater in a famine of that duration than when food is

plentiful throughout life.

Thus, famine shifts the happy medium toward favoring a more

painstaking development process. And since famines are unpredictable

events, occurring at irregular intervals, it's not possible for evolution to de

termine a species' ideal degree of perfectionism in advance: each individual

organism must have the ability to respond to its situation. Furthermore,

famines have always been like that, ever since organisms started eating other

organisms. It's therefore no surprise that, everywhere we look in nature, we

find the genetic machinery to respond to a famine early in life by slowing or

suspending growth.

You may know that nutrient deprivation in adulthood often has the same

effect to a milder extent, a phenomenon that doesn't seem to be explained by

what I've just told you. Indeed, there may not be such clear-cut evolutionary

reasons why adult-onset calorie restriction postpones aging at all. But there

don't need to be, because genetic programs that exist for one time or circum

stance are often activated unnecessarily in situations that are similar. Think,

for example, of the fact that startling someone causes a mild adrenaline rush,

something that exists to facilitate escape from life-threatening situations.

Finally I must explain why the logic I've outlined here implies that ma

nipulating these nutrient-sensing pathways isn't the most promising way to

postpone human aging. I actually have three reasons.

First, the degree of life extension that has been obtained thus far in

various species exhibits a disheartening pattern: it works much better in

shorter-lived species than in longer-lived ones. Nematodes, as I mentioned

above, can live several times as long as normal if starved at the right point in

their development; so can fruit flies. Mice and rats, however, can only be

pushed to live about 40 percent longer than normal. This pattern led me, a

few years ago, to wonder whether humans might even be less responsive

than that, and I quickly realized that there is indeed a simple evolutionary

reason to expect just such a thing. 1 2 It's a consequence of the fact that the


duration of a famine is determined by the environment and is independent

of the natural rate of aging of the species experiencing it.

Second, the adjustment of metabolism that organisms undergo when

food is scarce causes only a slowdown in the accumulation of molecular

and cellular damage, not a repair of damage that already happened. I've al

ready told you that the key "Eureka moment" in my development of SENS

was when I realized that repairing the damage of aging (before it progresses

into disease) might be simpler than preventing it—but even setting that re

alization aside, repair is bound to be preferable, simply because any feasi

ble therapy (whether to repair damage or to prevent it) will be only partial.

That's to say, repair therapies will repair some but not all damage, and pre

vention therapies will slow but not halt the accumulation of damage. Why

does this mean that repair is preferable? The logic is quite simple. In broad

terms, if you take a middle-aged person and halve the rate of their subse

quent aging, you'll double their remaining lifespan, but that might mean

adding only 20 percent to their total lifespan. By contrast, if you take that

same person at the same age and apply a therapy that halves their accumu

lated damage, and apply that same therapy periodically for the rest of their

life, you'll roughly double their total lifespan (because their accumulating

damage will only consist of the types of damage that your therapy can't re

pair), which means increasing their remaining lifespan (from the point

when you first applied the therapy) by a factor of maybe four or five! So

prevention-oriented approaches simply don't aim high enough.

But there's a third reason why I don't think nutrient sensing is the most

promising target for biomedical intervention in aging, and I would say it's

the most decisive. The reason it's been so incredibly easy to extend the lifes

pans of so many organisms by this one trick is because it's an evolved re

sponse to environmental conditions. The machinery that mediates that

response is fantastically complex and poorly understood, just like the rest

of our biology, but we can manipulate it easily despite that complexity, be

cause its initial step—the sensing of nutrient availability—is simple. Just as

you don't need to understand how your computer works to turn it on and

off, we also don't need to understand the process of how nutrient depriva

tion is translated into the adjustment of masses of interacting metabolic

pathways in order to turn that process on and off. But therein lies the show-

stopping problem. You may not need to understand how your computer

works in order to turn it on and off, but in order to make it do things that it

does not already contain the hardware and software to do, you have to un

derstand a lot more. And if the new functionality requires software that


hasn't yet been written or can't be installed, you have to understand a huge

amount more, enough to write that software yourself. The human body is, in

that sense, like a computer into which new software can't be installed—it's

very versatile, but that versatility cannot be extended by the same methods

that merely elicit the existing versatility. Therefore, we can be sure that there

is a fixed degree of life extension that can be achieved by manipulating the

nutrient sensing pathway—whether by calorie restriction (CR) itself, or by

drugs that trick the body into thinking it's being starved, or by genetic

changes that flip the same switch. As I explained a couple of paragraphs

ago, I think that ceiling is very modest, maybe only a two-to-three-year ex

tension; some of my colleagues think it may be as much as twenty to thirty

years—but it's still a ceiling. We will never be able to exceed that fixed de

gree of life extension by such means, however hard we try.

Not Good Enough—But Better than Nothing

I want to end this chapter on a positive note, though. Even though nutrient

sensing can only extend life by a fixed maximum amount, and even though

it may be a rather small amount, that's still better than nothing! Also,

there's a very general finding in laboratory life-extension experiments that

animals with some kind of mildly life-shortening genetic problem benefit

more from the therapy or regime than congenitally longer-lived individuals.

That's quite likely to apply to calorie restriction (CR) in humans, too—

which means that doing CR (or taking safe CR-mimicking drugs, as and

when they appear) may be a good insurance policy against unknown con

genital vulnerabilities. For these reasons, I strongly support the work that

many of my colleagues in biogerontology are doing to squeeze the most we

can out of that route to life extension.

But in closing, I want to bring you back firmly to the theme of this

chapter. Once upon a time, aging was a truly mysterious phenomenon, but

that time has passed. We can now reason about the aging of the human

body in just the same way, and with just the same confidence, as we can rea

son about the aging and decay of simple machines. We know why different

organisms age at different rates, whether that be because of different genes

or different environments. We know that our genes are our allies, not our

foes, in our war against aging—that they exist to postpone aging, not to

cause it, and we only age because those life-preserving genetic pathways are

not comprehensive.


Now—can you still tell yourself, with a straight face, that aging is too

mysterious to try to tackle? You may have just one straw to clutch at in your

effort to perpetuate your pro-aging trance: you may be telling yourself that

the devil is in the detail, detail that I have not yet provided. I'll be snipping

that straw in Chapter 4.

4

E n g i n e e r i n g R e j u v e n a t i o n

Let's briefly review what I've told you so far about aging. In a nut

shell, it's as follows:

• Aging is really bad for us, however much we like to forget the fact.

• Aging is not a mystery, and we can already postpone it a lot in the

• However, the techniques that have been so successful in the lab do

not seem promising for humans.

In this chapter I'm going to expand upon the "Eureka moment" that I re

lated in Chapter 1.1 will cover—in still broad, but somewhat more detailed,

terms—what each type of damage really is at the molecular and/or cellular

level, and also the broad strokes of how I think we can address that damage.

A Caveat: Why Prevention Is Usually Better than Cure

lab.

In Chapter 3,1 told you two heartening things about combating aging: firstly

that in principle it's no different than combating the aging of man-made

E N G I N E E R I N G R E J U V E N A T I O N 33

machines such as cars, and secondly that we've already discovered how to

postpone aging by a large factor in the laboratory. However, I then explained

that the second of these tidings of good cheer is actually going to be of only

very limited biomedical utility. Well, brace yourself, because I'm about to ex

plain that the first piece of good news is not so simple as it seemed, either.

I'll start with a rather more sobering thought about cars. Why are so

few of them maintained to an age far beyond that for which they were de

signed, even though we all know they can be?

There are two answers, one reassuringly inapplicable to the analogy

with human aging but the other very applicable indeed. The inapplicable

answer is: because their owners have the option of getting a new car. All

this says is that the chance that you will put in the effort and money to

maintain an old and declining machine depends on how much you are in

love with it. You may generally choose to junk your car when it starts to

malfunction because you're not very attached to it anyway, but if your

mother starts to malfunction and the wherewithal exists (even at a hefty

price) to repair her, it'll be a different matter.

The other answer is the problem: most people leave the serious

maintenance of their car until it's too late. It's obvious that the more

damage a machine sustains, the more work is needed to rectify that dam

age; but more than that, the technology needed to rectify it becomes

more and more sophisticated. When a car is really on its last legs, restor

ing it to full working order requires major attention—replacement of a

lot of parts, for example. And unlike the how-much-we-care argument

above, in this case the situation is absolutely the same for the human

body. The people who know this best are those who work not on the bi

ology of aging but on the medicine of aging: geriatricians. Geriatricians

try to help people whose aging has reached the point where physical or

mental function is appreciably impaired. They do their best to apply ex

isting medical technology to postpone the patient's further decline and

eventual death. But, as they know and as you also know, it's a losing bat

tle. The damage has already spun out of control: it's feeding back on it

self to accelerate the occurrence of additional damage, and the types of

damage that are occurring are becoming ever more numerous and var

ied. All the geriatrician can hope to deliver is a modest improvement of

the quality of life of the patient's last years, and perhaps a few months' to

a year's postponement of death. It's the age-old rule: Prevention is better

than cure.


But Only Usually . . .

But let's not leave it there. There's one thing about geriatrics that it has over

gerontology, and I hinted at it above: geriatricians use existing medical

technology. Why can they do that, when gerontologists can't?

The answer, when you think about it, is simple: To fix a problem that al

ready exists, you don't need to know how it arose. A car mechanic replacing

a car component doesn't need to know what type of corrosion wore through

a fuel line, or what size rock hit a windscreen; similarly, the geriatrician

doesn't need to know anything about free radical chemistry or cholesterol

metabolism in order to treat cardiovascular disease or diabetes. But by con

trast, preventing corrosion or shattered windscreens involves careful analysis

of the downstream side effects of salting roads and not clearing debris from

the highway; in the same way, the gerontologist needs to know a great deal

about extremely subtle and possibly hard-to-discover causal chains of events

in order to put "prevention is better than cure" into practice.

So, here we have two alternative approaches to postponing aging, one

preventative and one curative; I've explained a problem with each of those

approaches that makes them unpromising ways forward; and finally I've

pointed out that the problem that each approach has is not shared by the

other approach—preventing aging is soon enough but too complex, curing

the diseases of aging is simple enough but too late. Now, what does that say

by way of a possible way forward?

Worst of Both Worlds, or Best?

Well, I'll tell you what it said to me, that early morning in California.

Discussion during the day's roundtable-style sessions had focused on

the various theories of aging, and ways to prove or disprove them. This

mostly meant running through the multiple metabolic pathways that might

contribute to the development of aging damage. I had presented the case

that the production of free radicals by mitochondria—the tiny "power

plants" that extract energy from food and convert it into ATP, a form of en

ergy usable directly by the cell—is at the root of much of the aging process.

This was something that most of my colleagues suspected, but I had re

cently framed it in a novel way that reconciled some unexplained findings

in the field. I had confidence in my model, as it was my main specialist area

within gerontology at that time: a book-length treatment of it 1 had earned


me my Ph.D. But more important to me, it suggested a biomedical solution

to what I was convinced was a major cause of aging damage: With some

complex but foreseeable gene therapy, the connection between mitochon

drial free radicals and pathology could be severed, without the need to in

terfere with the mitochondria's normal energy-producing activity. (I'll say a

little more about this below, and lots more in Chapter 6.)

I had come to the conclusion that, in the best case, my mitochondrial

gene therapy proposal might (and I emphasize might) also slow the rate of

aging in humans attributable to most other causes by about 50 percent.

This would be a massive breakthrough, as it would lead to as good an ex

tension of healthy life as the most severe calorie restriction (even under the

CR optimists' scenario) but without CR's side effects. But I was far from

sure about that estimate, and in the wee hours of that morning, alone in a

hotel room, I was even less confident than usual, because I had spent all

day being reminded of just how many things go wrong in an aging body.

Many of these problems could be at least partly chalked up to the down

stream effects of the insidious, age-related increase in oxidative stress—the

imbalance between those substances in the body that tend to chemically

"need" electrons and substances that chemically "want" to donate them. I

believed my mitochondrial gene therapy proposal would nearly eliminate

this rise with age, but I couldn't be sure of just how much the rest of the ag

ing process would still go on without additional, targeted therapies—nor

what those therapies might be.

The candidates were numerous:

• Inflammatory enzymes essential to the immune system could also

oxidize cholesterol, particularly when there's a lot of it around,

contributing to atherosclerotic plaques.

• Our bodies' reliance on carbohydrates as a source of fuel exposes

us to the reactive chemistry of glucose, causing the "gumming up"

(glycation) of cellular proteins.

• Beta-amyloid, an aggregating protein, forms the basis of the "senile

plaques" in the brains of Alzheimer's patients. It is the result of ab

normal chopping-up of a normal precursor protein in the brain.

• The process of cell division gradually shortens each successive cel

lular generation's telomeres—the protective caps on the DNA dou

ble helix that serve the same function as the plastic bits on the end

of your shoelaces, preventing the chromosome from "fraying."

(See Chapters 10 and 12 for more.)


• Mutations in the cell's genetic database occur when, in the process

of creating needed copies of the DNA "instruction book" for the

new cell, the body's DNA-replicating machinery makes "typos."

• Tapping into the pools of stem cells (the primordial, unspecialized

cells that the body holds in reserve and causes to develop into par

ticular cell types as needed to replace cells lost to injury or disease)

gradually depletes what is, over a lifetime, a limited source of youth

ful cellular reinforcements.

The problem had me in its grip—and it wasn't just curiosity that was

keeping sleep at bay. While many of my colleagues viewed biogerontology

as a phenomenon to study for the sake of understanding it, I saw aging for

the humanitarian crisis that it is, the toll of tens of thousands of dead every

day ringing in my ears. Abandoning my first career in artificial intelligence

research, I had committed my life not just to alleviating the worst of the

morbidity and mortality of age-related disease, but to putting an end to the

entire horror show. I'd dedicated myself to the "engineering of negligible

senescence," as I had first termed the goal in my Ph.D. thesis—to the end

of aging.

But my inner dialogue that morning was leading to frustration, and

even some despair. Clearly, if real medical control of aging required cor

recting all of these potentially damaging metabolic processes individually,

real progress in anti-aging medicine might be like fighting the Hydra: no

matter how many heads you put down, more would spring up to take their

place. Normal metabolism is such an intricate, finely balanced web of reac

tions that tweaking one sends perturbations throughout the entire network,

usually creating new problems or negating the effect of the intervention by

eliciting a counterbalancing metabolic adjustment. For example, chronic

inflammation is a source of cellular damage. But if you interfere with in

flammation, you might impair immune defenses against pathogens. Equally,

free radicals—a by-product of your metabolism—cause oxidative stress

and damage over time. But crank up antioxidants, to defend against free

radicals, and you might help cancer cells to protect themselves against

chemotherapy drugs.

This process of dynamic metabolic adjustment is seen in the aging pro

cess, in fact. There are a number of aging changes that, while they might

have some pathological consequences, are not themselves forms of damage.

Putting it another way: they do not actually accumulate in the body's cells

and tissues; rather, they represent a shift in the equilibrium between creation


and destruction of the molecules involved. It seemed likely to me that such

changes, however harmful to the body's youthful functioning, were second

ary to something else. This meant that identifying and correcting that

"something else" would correct the maladaptive secondary change, render

ing moot the question of its contribution to the aging process. For instance,

the cell's ability to respond to many hormones and other signaling mole

cules tends to decline with age. But as we saw in Chapter 3, the logic of

evolution seems to dictate that this decline isn't programmed into the body.

It must therefore be secondary to some form of damage. Maybe the mem

branes of the cell lose their fluidity, impairing the ability of receptor mole

cules to change their shapes to pass on a signal. Maybe the machinery that

creates those receptor molecules becomes impaired. Whatever it is, identi

fying the damage itself would narrow the field of things that directly caused

such damage and that were thus at the root of aging.

And, come to think of it, there seemed to me to be far fewer kinds of

damage than processes that cause damage—hosts of different mutagens

and "pre-mutagenic" changes to DNA, for example, but only two types of

mutations: chromosomal and mitochondrial.

Well, I mused, that's a thought—just how many kinds of aging damage

ARE there? And are there similarly promising fixes for the rest of them?

There are mutations in our chromosomes, as I just mentioned; this sort

of damage causes cancer. I didn't (at that time—but see Chapter 12) have

any new proposals up my sleeve for that one; it was going to have to rely

(for now, at least) on other people's ideas. But there was no shortage of such

ideas: Cancer research is among the biggest fields in biomedicine.

What other problems could arise from nuclear mutations? It was

widely assumed that they were a major cause of age-related cellular dys

function, but I had been batting around a counterargument in my head for

some time—an argument that made me pretty sure that mutations not rele

vant to cancer would be irrelevant to aging within a currently normal life

time. Certainly, a noncancerous mutation in a single cell might make that

lone cell dysfunctional, but could it really substantially impact the tissue as

a whole? Clearly, if every cell in a tissue were misbehaving, a person would

be in trouble—but that can't be the case. Why not? Well, if it were that

easy for an average cell to pick up a mutation, then everyone would be rid

dled with cancer by the time they were adults, because it takes just one can

cerous cell to be allowed to grow to make a life-threatening tumor. What

that suggested was that nearly all cells are kept genetically intact into and

beyond a person's forties, and that the great majority of cells continue to be


so throughout the "normal" life span. In other words, in order to prevent

us from dying of cancer before puberty, our DNA maintenance machinery

has to be so good that mutations not relevant to cancer just don't happen

often enough to matter. Better yet, the exact same logic seemed to work for

what biogerontologist Robin Holliday had memorably termed "epimuta-

tions"—changes not to the DNA sequence itself, but to the structure of the

individual bases or the proteins around which the double helix is normally

wrapped. Epimutations can do great harm, because they change the rate at

which genes are decoded into proteins, but epimutations can cause either

cancer or other problems, just as bona fide mutations can, so the "cancer is

a bigger problem than anything else" conclusion applies to them too. I'll

tell you more about this line of reasoning in Chapter 12.

In addition to chromosomal mutations, there are mitochondrial muta

tions, which may be a major part of the problem caused by free radicals.

(Mitochondria are the only cell components that contain their own DNA

independently of our chromosomes.) Luckily, I thought, I believe I already

know a feasible solution to mitochondrial mutations. My solution was totally

unlike the problematic approaches that were being proposed by other re

searchers, and I felt that it was much more powerful. It didn't rely on

souped-up antioxidant defenses, an idea which was still being pursued not

only by vitamin salespeople but even by some biotech companies. (This de

spite the fact that biogerontology specialists had long ago concluded that

antioxidants are a dead end after they had failed, again and again, to affect

aging one whit. 2 A better demonstration that our ambivalence about aging

is only skin deep is hard to find.) Free radicals are just too reactive to be ef

fectively mopped up with vitamins, nor even with the novel free radical

scavengers that were coming out of pharmaceutical labs around this time

(with names like MnTBAP and EUK-134, synthetic versions of the antiox

idant enzyme superoxide dismutase). Or if not too reactive, they might be

too necessary—-it had recently become clear that cleaning up too many free

radicals would cause new headaches for the body. After millennia of expo

sure to their reactive chemistry, evolution has learned to harness free radi

cals as signaling molecules, 3 so a heavy-handed repression of the cell's

exposure to them would actually harm cellular metabolism, not aid it. The

body might even react to antioxidant supplements by reining in its natural

antioxidant defenses to compensate.

Trying to reduce free radical production was a job that many of my col

leagues considered to be the best way to slow down aging damage, but (for

the reason just given) actually pulling it off without seriously impairing the


organism's ability to carry on with life's many duties would be extremely

tricky. Not only that, most free radicals are produced in the mitochondria

in the process of making ATP from food energy, and trying to mess around

with that central feature of metabolism is bound to create side effects.

As I alluded to a few paragraphs ago, I had already proposed avoiding

these problematic approaches by a strategy I'll cover in detail in Chapter 6.

Briefly, the idea is to let metabolism proceed as normal—accepting that

some free radicals will be generated and some biomolecules damaged—but

to sever the link between free radicals and oxidative stress at its nexus. In

my Ph.D. thesis, I had argued that (contrary to the prevailing view at that

time) mitochondrial free radicals do not drive a systemwide rise in oxida

tive stress with age by damaging the rest of the cell directly. Instead, the

damage that they cause to the mitochondrial DNA causes the mitochondria

to enter a maladaptive state that spreads oxidative stress out beyond the

cell. This, I had reasoned, meant that scientists could solve the problem of

mitochondrial mutations by copying mitochondrial DNA from its vulnera

ble spot at "ground zero," within the free-radical generating mitochondria,

into the bomb shelter of the cell nucleus, where damage to DNA occurs far

less frequently. The proteins they encoded would have to be constructed in

a manner that induced the cell to transport them to mitochondria, but the

procedure to achieve that had been mostly understood for some time. In

this scenario, the nuclear copies would act as a "backup" for the mitochon

drial DNA: the mitochondria could operate as normal even if their DNA

became damaged, so they would not cause long-term harm to the organism

as a whole. Mitochondria would still suffer damage, but would not enter

the maladaptive state I just mentioned, so they would not cause the creep

ing, destructive slide into oxidative stress in the rest of the body.

Okay, two down (chromosomal and mitochondrial mutations); how

many to go? There is glycation, the warping of proteins by glucose. Well,

that seemed relatively easy, because it was well known in the field that

a biotech startup called Alteon was already running clinical trials using

a compound called ALT-711, which appeared to reverse the protein cross-

linking that this process caused. While the effect was weak, it was signifi

cant: the compound had a limited ability to restore some of the flexibility

that's lost to glycation with age in the heart and blood vessels, and also

showed promise for kidney damage in diabetics. It was proof-of-principle

that without interfering with glucose metabolism, you could allow the for

mation of protein cross-links but prevent the pathological results by undo

ing the damage after the fact. (This is an important and common theme, as


you will see—don't interfere with the process, but rather repair or clean up

the damage that has accumulated.) See Chapter 9 for lots more detail about

the glycation problem.

What else? There are the various kinds of junk that accumulate outside

the cell: beta-amyloid, the lesser-known transthyretin, and possibly other

substances of the same general sort. Here again, recent studies in the pri

vate sector—this time by a Californian company named Elan—had shown

that you could actively remove the problem, in this case by vaccinating mice

against the amyloid plaque and letting their immune cells gobble the stuff

up. The concept had shown such rapid success in the lab that it was already

close to clinical trials. Will I be telling you more about this, later in the

book? You bet—see Chapter 8.

We must also address the unwholesome goo that builds up within the

cell, such as lipofuscin. I started to get quite excited at this point, because

just a year previously, in Dresden in June 1999, I'd come up with a new

proposal to eliminate such material, involving the identification and engi

neering of enzymes from soil bacteria. (This was a classic case of someone

not immersed in their own experimental work being able to bring together

ideas from very distant disciplines to form a new approach to an existing

problem—a critical element of modern scientific progress, which has been

sadly neglected in many areas of medicine and biology.) The concept of us

ing soil bacteria to degrade long-lived organic material had been around for

decades, but not in gerontology, or even in any biomedical field. Rather, it

was a mainstay of environmental decontamination, where it is known as

"bioremediation." No one in gerontology had really even heard of it, let

alone seen its biomedical potential. If you're intrigued, well, you only have

to wait until Chapter 7.

Another item that must be added to the list is cellular senescence, the

"aging" of individual cells. Senescence, in this meaning of the word, is a

state of arrested growth in which the cell produces chemical signals dan

gerous to their neighbors. In theory, at least, there are all kinds of ways to

deal with cellular senescence, though I wasn't sure which of them would ul

timately pan out. Senescent cells express distinctive marker proteins, which

should allow them to be targeted for selective destruction. Alternatively,

once researchers tease out the damage or gene expression shifts that keep

cells locked in this abnormal, arrested state, it might be possible to restore

senescent cells to normal functionality. This was all still speculative, of

course, but Judy Campisi at Berkeley and others were already hot on the

trail. Chapter 11 will reveal all.

E N G I N E E R I N G R E J U V E N A T I O N 4 1

There's also the depletion of cells—of nondividing cells like neurons or

heart cells, which are not naturally replaced when they die, and also the

more paradoxical depletion of stem cell pools essential to healing and main

tenance of tissue. Anyone who'd read a newspaper in the previous few years

knew that scientists were hotly pursuing a way to deal with the age-related

loss of cells, including stem cells: more stem cells, cultured in the lab and de

livered as a rejuvenating cellular therapy. There were several viable ap

proaches to this, different ones probably suited to different conditions. One

was extracting the adult stem cells already in the patient, growing more of

them, and then reinfusing them into the patient. Another was harvesting

some of the more versatile embryonic stem cells that were already sitting,

waiting to be thrown out as medical waste, in fertility clinics all across the

world. The most complex was "nuclear transfer," in which a person's old,

specialized cells could be transformed into young, versatile stem cells again

via the environment of a woman's egg and a quick jolt of electricity. Re

searchers were already showing in animal models that these cells could be

used to cure age-related diseases and trauma, and there was every reason to

expect that the same techniques, once perfected, could be used to replace

cells lost to age-related decay.

What else? Er . . .

I couldn't think of any more categories of damage! Try as I might, I re

ally couldn't. There were a couple of other examples of molecular changes

that accumulated throughout life, but I had reasons to believe that they

were in the same boat as non-cancer-causing chromosomal mutations: they

might be harmful if we lived hundreds of years, but they very probably

weren't harmful in a normal lifetime. Other than that, everything I had

learnt about during my five years of study and conference-hopping seemed

to be covered.4

I stepped back for a moment and articulated the logic I had been de

veloping those past few hours. At root, I was addressing a simple question:

if geriatrics fails because prevention is better than cure, and gerontology

fails because our understanding of metabolism is so limited, then might an

intermediate target be the best of both worlds? Might it be possible to re

pair damage after it's been laid down (hence avoiding the need to under

stand the details of how it's laid down) but before it spirals out of control

(hence also avoiding the losing battle that is geriatrics)? See Figure 1.

I could only answer this question in the affirmative if I could make a

specific, extremely bold claim: that these intermediates, these proximate

side effects of metabolism that accumulate in the body throughout life,


Figure 1. The "engineering approach" that I conceived in June 2000, as an intermediate, best-of-both-worlds alternative to gerontology and geriatrics as a strategy to combat aging.

could all be either (a) ruled out of relevance to late-age pathology (as I felt

I could do for mutations that don't cause cancer) or (b) repaired or made

harmless by foreseeable therapies. If some could be repaired, and some

were definitely harmless or could be made so, but some fell into neither

such category, the idea would fail. Like any machine, the body is only as ro

bust as its weakest link, so partial maintenance will have little or no effect

on longevity.

But I went over my list again and again, and as I did so I became ever

surer that there was no clear-cut exception. The combination of my own

idea for eliminating intracellular garbage, the idea I'd been championing

for a few years for making mitochondrial mutations harmless, and the vari

ous other therapies being worked on around the world to address glycation,

amyloid accumulation, cell loss, senescent cells, and cancer . .. that was re

ally and truly an exhaustive list. Figure 2 shows my enumeration of the

problems and solutions that constitute the SENS (Strategies for Engi

neered Negligible Senescence) plan as it stands today.

As I mentioned above, there may well be other problems that will

emerge if we succeed in solving all of these and thereby live a great deal

longer. I felt, however, that my list might very well be comprehensive

enough to give a few decades of extra life to people who are already in mid

dle age before we start the treatments. And that was certainly a much more

promising first step than anything that my colleagues had reviewed the pre

vious day or in the many conferences and articles that I'd devoured over the

previous few years.

The California sun was rising, and with it my spirits. It was clear that


Damage Could be fixed or

made harmless by For details see chapter

Cell loss, cell atrophy Cell therapy, mainly 11

Junk outside cells Phagocytosis by immune

stimulation

8

Crosslinks outside

cells

AGE-breaking

molecules/enzymes 9

Death-resistant cells Suicide genes,

immune stimulation 10

Mitochondrial

mutations

Allotopic expression of

13 proteins 5.6

Junk inside cells Transgenic microbial enzymes 7

Nuclear [epi]

mutations (only

cancer matters)

Telomerase/ALT gene

deletion plus periodic stem

cell reseeding 12

Figure 2. The seven parts of SENS.

daunting technical hurdles would need to be overcome if the therapies I

envisaged were to start saving lives in the real world. But even so, I recog

nized that the line of thought I'd followed had the potential to paint the

broad strokes of a revolution in biogerontology—and hopefully, in due

course, in the future of human life. Repairing (or, in the case of mitochondr

ial mutations, obviating) accumulating damage was a genuine best-of-both-

worlds middle ground between the traditional gerontology and geriatrics

approaches. It focused on a weak link in the chain of events leading from me

tabolism to pathology: it was early enough in that chain to avoid the down

ward spiral that doomed geriatrics to be forever a losing battle, but yet it was

late enough in the chain to avoid the perturbation of metabolism that

doomed the "over-preemptive" gerontology approach.

This idea would be easily grasped by my former colleagues in the com

puting field, or indeed by most engineers. In engineering, it's routine to de

sign technologies before a full theoretical understanding of the underlying

physics is achieved. Engineers were making workable use of electricity, su

perconducting magnets, and even nuclear energy (in the form of weapons)

long before they had a coherent theoretical explanation for the forces they


were manipulating. Even in medicine, the effective use of treatments had his

torically often long preceded our mechanistic understanding of them. Salicy

lates from willow bark have been used as anti-inflammatory treatments for

centuries, and Bayer chemist Felix Hoffmann was even able to modify these

natural compounds to make them more palatable and less prone to upset the

stomach, yet the molecular basis for the action of the new wonder drug (as

pirin) would not be understood for seven decades. Of course, even more ef

fective drugs can often be designed from the ground up once the key

enzymes and genes upon which they might act are sequenced—but that level

of detail was not needed to get started in developing effective medicines.

Making this reorientation was dizzying—but once you accepted it, I re

alized, the whole project suddenly became tractable, and the way forward

clear. You could stop thinking of aging as a hopelessly complex theoretical

problem to solve, and get on with attacking it head-on, as an engineering

challenge that needed to be overcome. "Engineered negligible senescence,"

a phrase that I'd previously used offhandedly, suddenly presented itself as

the most precise description possible of the task ahead. 5

In fact, I realized, the problem might even be thought of in terms of the

way we prevent "aging" in other physical structures, such as houses or cars.

As I discussed in Chapter 2, evolution's priorities for nearly all organisms

stop them from living indefinitely without aging: mutations in the genes in

volved would not be removed by selection when the ageless organism was

eaten by predators or otherwise succumbed in just a tiny fraction of "for

ever." This is much like cars, which are designed to meet the opposing pri

orities of durability and low cost at some midway point that is acceptable to

the consumer. Thus, our bodies—like our other vehicles—are designed to

survive for a biological "warranty period": they are given enough robust

ness and self-repair capability to function at peak performance for as long

as they can reasonably be expected to stay alive in the wild, but no longer.

But of course, individual users of cars or of bodies may have very dif

ferent priorities from those of Detroit or of our "selfish genes." If you want

a car to last much longer than manufacturers of cheap cars typically intend,

you have two options. One is to pick up a better model in the first place:

buy yourself a Volvo instead of a Chevy Cavalier. This is all well and good

for cars, but it isn't an option for those of us who have only the genes we

were born with. And of course, even Volvos will still eventually break

down, only a few years after a more economical product would do.

That's why, when we want to keep a car on the road for an exception

ally long time, we actually choose the other option: we fix damage as it hap-


pens. Whether it's a poor laborer keeping his ancient VW bug running be

cause it's the only car that he'll ever be able to afford, or a wealthy collector

maintaining an old MG for the sheer love of it, we all know that a car can

be kept going more or less indefinitely with sufficient maintenance. We

don't have to keep the cars off the road in climate-controlled garages, and

we don't rely on the latest gasoline additive: we simply repair worn-out

parts when they begin to fail. As I saw then, and as I will describe in the

chapters ahead, the analogy to humans (at the cell, tissue, and organ level)

is strikingly exact.

The Devil Is in the Detail

At the end of Chapter 3,1 explained that the purpose of this chapter would

be to remove people's last hope for maintaining their pro-aging trance: the

belief that my breathlessness about the recent progression of aging from

mysterious to manipulable might be all talk and no substance. I hope I've

done that—but I've come up against the pro-aging trance often enough to

know it's sometimes very hard to break.

That's why, for most of the rest of this book, I'll be wading deep into

the fine scientific detail of the seven SENS categories and the remedies for

them. I know that most readers of this book will not be scientists, so this

may be intimidating. But Michael Rae and I have worked hard in Part 2 to

present cutting-edge science in a manner comprehensible to any educated

layman who's willing to put in the time to read it carefully. I therefore urge

you to dive in and learn in detail about the types of damage that comprise

aging and the foreseeable technologies that will, I am confident, enable us

to repair or obviate that damage comprehensively enough to avoid age-

related physical and mental decline indefinitely.

M e l t d o w n o f t h e C e l l u l a r

P o w e r P l a n t s -

The cellular components—"organelles"—known as

mitochondria play a large role in aging, hand in hand with

reactive chemicals known as free radicals. When I came into the

field in the mid-1990s, however, this role was not clearly defined;

evidence and interpretations were contradictory and awaiting

synthesis. In response, I developed what is now a widely

accepted mitochondrial free radical theory of aging. Read on: In

order to understand aging, you must understand a little of the

way in which our cells work.

In Chapter 4. I explained that there are seven major classes of life

long, accumulating "damage" that we must address if are to uncouple their

causes—the processes of life—from their eventual consequences, the pathol

ogy of aging, and thereby prevent those consequences. Six of those seven are

the subject of one chapter each in this part of the book—Chapters 7 through

12. But the first one I'm going to address, mitochondrial mutations, is going

to take two chapters. That's because the question of whether mitochondrial

mutations matter at all in aging is actually a really complicated one, and we

must do our best to answer it in order to know whether we need to worry

about them. Remember that in Chapter 4, I briefly noted that SENS does not

incorporate a plan to address mutations in our cell nucleus at all unless they

5


cause cancer, because non-cancer-causing mutations accumulate too slowly

to matter in a normal lifetime. (I will explain this logic much more thoroughly

in Chapter 12.) A lot of gerontologists feel that way about mitochondrial mu

tations. I disagree with them, so I need to tell you why. For each of the other

six SENS damage categories, by contrast, there's no argument: at least one of

the major pathologies of aging is clearly caused or accelerated by that type of

damage. So those six categories will only require one chapter each, focusing

mainly on the solution and with a relatively brief description of why there's a

problem to solve.

Free Radicals: A Brief Primer

Almost everyone has heard of free radicals by now. Their involvement in ag

ing is asserted so often and so confidently in popular press articles—

especially articles trying to promote the latest "antioxidant" nutritional

supplement—that you'd think the matter was done and dusted. As we'll

see, however, the exact roles played by free radicals in the aging process—

and the best ways to deal with the problems they cause—are a lot more

complicated, and more controversial, than these articles let on.

Free radicals in biology are, for the most part,1 oxygen-based molecules

that are missing one of the electrons in their normal complement. Electrons

are charged particles that surround the central nucleus of the atom, and they

occupy well-defined locations (you can think of these as distances from the

nucleus) termed orbitals. By their nature, molecules can only remain chemi

cally stable when each of the electrons in the orbitals of their constituent

atoms has a paired twin to complement it; an orbital with only one electron

is unstable. So when a molecule loses one half of an electron twosome, it be

comes chemically reactive until it gets that electron back. Usually, the free

radical's stability is restored when it tears an electron out of the nearest avail

able normal, balanced molecule—but with this electron stolen from it, that

second molecule generally loses its chemical stability, and will seek in turn to

restore its balance by a similar theft. It's a chain reaction.

Some unusual molecules—antioxidants—finesse this logic and are rel

atively stable even when they contain an unpaired electron. These mole

cules can "quench" free radical chain reactions. Until they do, however,

free radicals will tear their way through your body like biochemical vandals,

trashing whatever essential biomolecule they bump into: the structural pro

teins that make up your tissues, the fatty membranes that compartmental-

M E L T D O W N O F T H E C E L L U L A R P O W E R P L A N T S 5 1

ize and facilitate your cells' various specialized functions, the DNA code

that holds the blueprints of the enzymes and proteins required by the cell,

and so on. In biology, function follows structure, so the ability of these mol

ecules to support metabolism and hold you together is impaired when they

are chemically deformed by this process.

This is obviously not good for you—and unfortunately, it's unavoid

able. Free radicals are part of being alive.

While popular press articles on aging often give the impression that free

radicals come mostly from environmental pollutants or toxins from an im

pure diet, the fact is that the overwhelming majority of the free radicals to

which your body is exposed are generated in your very own cells—in the mi

tochondria, our cellular "power plants." Mitochondria are one of several

types of "organelle," or self-contained cellular component that exists out

side the nucleus. Each cell has hundreds to thousands of mitochondria.

Man-made power plants take energy that is locked away in an inconvenient

form of fuel—such as coal, natural gas, the strong nuclear force which holds

atoms together, or wind—and convert it into a more convenient medium,

electricity, which you can use to run your blender or computer. In just the

same way, mitochondria convert a difficult-to-use energy source (the chemi

cal energy locked up in the glucose and other molecules in your food) into a

more convenient one: adenosine triphosphate, or ATP, the "universal energy

currency" that your cells use to drive the essential biochemical reactions that

keep you alive.

Mitochondria generate most of their cellular power using almost identi

cal principles to the ones used by hydroelectric dams—right down to the

turbines (see Figure 1). Using a series of preliminary biochemical reactions

(each of which generates a small amount of energy), energy from food in the

form of electrons is transferred to a carrier molecule called NAD+ (and a

similar one called FAD). These electrons are used to run a series of "pumps"

called the electron transport chain (ETC) that fill up a "reservoir" of protons

held back by a mitochondrial "dam" (the mitochondrial inner membrane).

The buildup of protons behind the "dam" creates an electrochemical

force that sends them "downhill" to the other side of the mitochondrial in

ner membrane, just as water behind a dam is drawn downward by gravity.

And just as a hydroelectric dam exploits the flow of water to run a turbine,

the inner membrane contains a quite literal turbine of its own called

"Complex V" (or the "F0/F1 ATP synthase") that is driven by the flow of

protons. The rushing of protons through the Complex V turbine causes it

to spin, and this motion is harnessed to the addition of phosphate ions


Figure 1. The F 0 / F 1 ATP synthase.


("phosphorylation") to a carrier molecule ( a d e n o s i n e diphosphate, or

ADP), transforming it to ATP.

Unlike hydroelectric dams, however, the use of chemical energy in food

to generate ATP via this system is a chemical reaction. As with the burning of

coal or wood to release energy, the powering-up of ADP into ATP consumes

oxygen, which is why we have to breathe to keep the whole system running:

oxygen is the final resting place of all those electrons that are released from

food and channelled through the proton-pumping electron transport chain.

Thus, the whole cycle is called oxidative phosphorylation (OXPHOS).

But while hydroelectric dams are (for the most part) environmentally

benign, mitochondria are in one key aspect more like conventional power

sources. Just like coal or nuclear power plants, mitochondria create toxic

wastes during the conversion of energy from one form into another. As the

proton-pumping complexes of the electron transport chain pass electrons

from one to the next, they occasionally "fumble" an electron here or there.

When this happens, the electron usually gets taken up by an oxygen mole

cule, which suddenly finds itself with an extra, unba l anced electron. (I just

mentioned that oxygen is also the sink for the electrons that are not

fumbled—that are properly processed by the mitochondria—but that pro

cess loads four electrons onto each oxygen molecule, not just one, so there's

no problem of electron imbalance.) Adding one electron, by contrast,

transforms benevolent oxygen into a particularly important free radical, su

peroxide. With your mitochondria generating ATP day and night continu

ally, the ongoing formation of superoxide is like having a constant stream of

low-grade nuclear waste leaking out of your local reactor.

Once scientists established that mitochondria were the main source of

free radicals in the body, it was quite quickly realized that these organelles

would also be their main target. Free radicals are so rabidly reactive that

they never travel far, attacking instead the first thing that they come

across—and the mitochondria themselves are at ground zero. And there are

plenty of potentially sensitive targets for these radicals in the mitochon

drion. Free radicals p r o d u c e d in the mitochondria are right next to the very

membranes and proteins on which ATP production depends, and also

within spitting distance of the mitochondrial DNA. What's that, you say?

Well, whereas other components of the cell have all their proteins coded for

them by the cell's centralized genetic repository in the nucleus, mitochon

dria have their own DNA for thirteen of the proton-pumping, ATP-

generating proteins in their membranes. 2 If that DNA is significantly

damaged, the mitochondrial machinery will go awry. Unfortunately, it's


clear that mitochondrial DNA does suffer a lot of self-inflicted damage,

taking as much as a hundredfold more initial oxidative "hits" than the cell's

central, nuclear DNA, and suffering many times more actual, enduring mu

tations with age.

Starting with a classic paper put out in 1972 by chemist Denham Har-

man 3 (who already had the distinction of being the father of the original

"free radical theory of aging"), researchers put these facts together with a

range of experimental findings and came up with several variations of a

"mitochondrial free radical theory of aging." Let's briefly survey that exper

imental evidence. 4

First of all, there was evidence from comparative biology. Slower-aging

organisms, relative to faster-aging ones of similar size and body tempera

ture, are always found to have slower mitochondrial free radical damage ac

cumulation. They produce fewer free radicals in their mitochondria; they

have mitochondrial membranes that are less susceptible to free radical

damage; and sure enough, they accumulate less damage to their mitochon

drial DNA. Calorie restriction (CR)—the only nongenetic intervention

known to slow down aging in mammals—improves all of these parameters:

it lowers the generation of mitochondrial free radicals, toughens their mem

branes against the free radical assault, and above all it reduces the age-

related accumulation of mitochondrial DNA mutations—the irreparable

removal or overwriting of "letters" in the genetic instruction book.

Leading toward the same conclusion from the opposite direction, CR

does slow down aging, yet it has no consistent effect on the levels of most

self-produced antioxidant enzymes. The enzymes that people examined in

this regard in the 1980s were ones that are found predominantly in the rest

of the cell, not in the mitochondria. This again suggests that free radical

damage outside of the mitochondria is not a directly important cause of ag

ing, since aging can in fact be slowed down (via CR) without doing the one

thing that would most directly interdict that damage.

Fast-forward, for a moment, to 2005. In that year, the most direct evi

dence so far on this point came to light. It involved mice that had been

given genes allowing them to produce extra amounts of an antioxidant en

zyme (catalase), specifically targeted to different parts of their bodies. 5 , 6

There was little to no benefit provided by giving these organisms catalase to

protect their nuclear DNA—the genetic instructions that build the entire

cell and determine its metabolic activity, except for those parts that the mi

tochondria code for themselves. And there was also no benefit observed

from targeting catalase to organelles called peroxisomes, which are involved


in processes that produce hydrogen peroxide (the molecule that catalase

detoxifies) and accordingly are already stoked up with the enzyme. Yet,

delivering catalase to the animals' mitochondria, which significantly re

d u c e d the development of mitochondrial DNA deletions, extended their

maximum lifespan by about 20 percent—the first unambiguous case of a

genetic intervention with an effect on this key sign of aging in mammals.

These mice were no more than a twinkle in their creators' eyes a de

cade ago, when I first addressed the question of mitochondrial oxidative

damage. But even back then, it seemed unassailable that free radical dam

age to the mitochondria was a key driver of aging. The question was: what

linked the one to the other?

That might sound like a stupid question, given that free radicals are ob

viously toxic, but it turned out to be decidedly tricky to come up with a co

herent, detailed, mechanistic explanation for the connection. Scientists

convinced that mitochondrial free radicals play a role in aging all begin with

the undeniable observation that free radicals spewing out from the mito

chondrion damage the membranes and proteins that it needs to generate

ATP, and also cause mutations in the mitochondrial DNA that codes for

some of those same proteins. But any such theory must explain how this self-

inflicted damage contributes to the progressive, systemic decay that consti

tutes biological aging. Until recently, nearly all such theories postulated the

existence of some form of mitochondrial "vicious cycle" of self-accelerating

free radical production and bioenergetic decay. 7 , 8

In these highly intuitive schemes, the mitochondrion is pictured to be

like a hydroelectric dam whose turbines become rusted, worn, or broken

by the forces to which they are subjected every day. Thanks to free radical

damage to their membranes, proteins, and DNA, mitochondria in cells

throughout the body would become progressively less able to pump pro

tons and to keep a lid on the "hot potato" chain of ATP synthesis with age,

leading to inefficient energy generation and increased production of free

radicals as more and more electrons escape from increasingly banged-up

transport complexes. Thus would begin the "vicious cycle," as more and

more renegade electrons tore into more and more mitochondrial con

stituents, leading to further damage to those same constituents, causing yet

more inefficient, dirty energy generation, and so on and so forth, spiralling

downward and ultimately starving the cell of energy and rendering it a haz

ardous waste site. See Figure 2.

Some version of this scenario is repeated in nearly all popular books and

articles about the role of mitochondria in aging, as well as most scientific


Figure 2. The "vicious cycle" theory of mitochondrial mutations accumulation. The key tenet of the theory is denoted by the asterisk: that typical mitochondrial mutations raise the rate of release of free radicals.

journal publications. Yet we've had evidence for nearly twenty years show

ing conclusively that it can't be right.

Everything You Know Is Wrong

The "vicious cycle" theory of mitochondrial decay paints a picture that

sounds seductively plausible, but it just isn't compatible with the data. While

many scientists remain oblivious to the glaring inconsistencies in these theo

ries even today, a few mitochondrial specialists and biogerontologists have

been pointing these problems out since the mid-1990s. So different were the

predictions of "vicious cycle" theories from the experimental findings that

many of these researchers went so far as to suggest that the findings simply

M E L T D O W N O F T H E C E L L U L A R P O W E R P L A N T S 57

ruled out a role for mitochondria free radicals in aging—forgetting that such

a role might exist but not via a vicious-cycle mechanism.

The first problem with at least some versions of the vicious cycle the

ory had actually been pointed out decades earlier—just after Harman had

originally put forward the first version of the mitochondrial free radical the

ory, in fact—by none other than Alex Comfort. (Yes, that's the same Alex

Comfort who wrote The Joy of Sex. He was a true polymath: he was also a

controversial anarchist agitator, a poet, and a highly distinguished biogeron-

tologist.)

In 1974, Comfort pointed out that while each mitochondrion could

temporarily suffer progressively increasing damage to the proteins and

membranes that make up its ATP synthesis machinery from the ongoing

free radical barrage, no theory based on the idea that this damage would

get worse and worse with age could fly, for the simple reason that the cell is

constantly replacing and renewing those very components.

Periodically, old mitochondria are tagged for destruction in yet an

other type of organelle, the lysosome (the cellular "toxic waste incinera

tor," about which I'll be talking a great deal in Chapter 7). Then, to make

up for the loss of energy factories, the cell puts out a signal for the remain

ing mitochondria to replicate themselves. During replication, each mito

chondrion duplicates its DNA, and then that essential core "grows" itself

a new "body," including pristine new proton-pumping proteins and mem

branes. Whether you're five years old or fifty, any given mitochondrion in

your cells contains membranes and proteins that are on average only a few

weeks old. Thus, the newest and the oldest of these mitochondrial compo

nents are present in the same proportions in the very old as in the very

young. It just can't be that aging is driven by a progressive process of de

generation in components that undergo a continuous process of renewal.

However, this objection wasn't necessarily a problem for the more pop

ular versions of the vicious cycle theory: those that assert that free radical

damage to the mitochondrial DNA drives aging. Although mitochondrial

membranes and proteins are periodically replaced, all mitochondria inherit

their DNA directly from their "parent" power plants, which faithfully copy

out their DNA and pass it on to their "children"—and just as whole organ

isms pass on any mutations that they may harbor in their DNA to their off

spring, so errors in "parent" mitochondria appear in the next mitochondrial

generation. If the mitochondria that have damaged DNA are preferentially

destroyed by lysosomes, the effect will be as before—damage will be


removed as fast as it spreads—and that's what Comfort reasoned would be

occurring. But if there's no such bias in which mitochondria are and are not

destroyed, DNA damage will accumulate.

These theories received a superficial plausibility boost from studies

conducted in the 1990s, which showed that aging bodies do, indeed, accu

mulate cells populated with mutant mitochondria. However, the same stud

ies shot entirely new—and even more deadly—holes into mitochondrial

DNA-based "vicious cycle" theories.

For one thing, it was found that all of the mutant mitochondria in a given

cell contain the same mutation. This is exactly the opposite of what the "vi

cious cycle" would predict. If each mitochondrion individually decayed as a

result of a self-accelerating cycle of oxidative "hits" to its DNA, then each

one would display an unique, random profile of mutations. In the same way,

if one day—independently—two disgruntled librarians were each to snap,

going on automatic rifle rampages through the collections in their care, you

would naturally expect to see that the bullets would have hit different books,

even if the collections themselves were the same: one would have put a bullet

straight through the spine of a copy of Finnegans Wake, while the other

would have punched an off-center dot atop the " i" in Bridget Jones' Diary,

and so on, at random, until each mad bibliophile ran out of bullets.

Instead, wherever cells that contain defective mitochondria are found,

the mutants all harbor an identical DNA mutation. It's as if librarians across

the state had marched into work and each fired his or her guns exactly

once, in every case into copies of The Catcher in. the Rye. Random muta

tions happening continuously in each mitochondrion cannot reasonably re

sult in each of the damaged mitochondria in a cell containing the same

error in their DNA; a random mutation-creating process can't explain the

complete takeover of cells by such mitochondria, or the presence of other

cells that contain nothing but healthy ones.

In fact, it's even weirder than that, because the presence of mutant mi

tochondria turns out to be an all-or-nothing affair. That is: near enough, not

only do all of the mutant mitochondria in a given cell turn out to contain

the exact same mutation, but those cells that harbor any damaged mito

chondria are found to contain nothing but mutants—while the other cells

have nothing but pristine, youthful "power plants."

But wait: the findings are even more bizarre yet. While each cell is full

of mitochondria that all bear the same mutation, the mitochondria in dif

ferent cells contain different mutations. It's as if all of the librarians in

Delaware had pumped their local branch's copies of War and Peace full of


lead, while their colleagues in California had simultaneously displayed an

equally single-minded determination to purge their collections of Lady

Chatterly's Lover. It's a case in which even the most skeptical conspiracy-

theory debunker would be f o r c e d to admit that a "random act of violence"

was not a credible explanation for the crime scene.

The nature of these mitochondrial mutations also proved to be inconsis

tent with vicious cycle theories of mitochondrial priority in aging. The as

sumption had been that damage to the DNA blueprints for mitochondrial

proteins would most often result in minor defects in the instructions by

which those proteins are coded. The ensuing proteins would be close

enough to their proper structure to remain more-or-less capable of carrying

on, but would be dysfunctional, "fumbling" more electrons into free radi

cals and generating less ATP. Instead, the mutations that accumulate in cells'

mitochondria were found to be overwhelmingly deletions of large blocks of

DNA, which completely shut down the creation of all the mitochondrially-

encoded proteins.

The vicious cycle theory proposed that mitochondria would make pro

gressively less ATP and more free radicals as they accumulated more and

more of these defects in their DNA. Instead, it was found that mutant mi

tochondria produce essentially no free radicals, and that the change in each

mitochondrion could be attributed to a single, catastrophic event, rather

than to a "death from a thousand cuts."

Forget the Quality, Feel the Quantity

An additional finding seemed to leave no room for any way, vicious or oth

erwise, in which mitochondrial mutations could be involved in aging: very,

very few cells actually contain mutant mitochondria at all. The vast majority

of cells remain in perfect mitochondrial health well into old age. Yes, a tiny

proportion of older people's cells—about 1 percent—could be shown to be

completely taken over by mitochondria that all suffer from an identical de

fect in their DNA; but 99 percent of cells were fine. How could 1 percent

of cells matter?

Many biogerontologists concluded that these findings put the kibosh

on any theory that asserted that mitochondrial decay was important in ag

ing. If nearly every cell in the body still enjoys the same level of ATP output

as it had in its youth, and suffers no more free radical damage than it did in

its prime, how could a tiny proportion of cells that are low on power, but


whose mitochondria produce no more free radicals than their neighbors—

in fact, produce no free radicals at all—possibly have much negative effect

on the function of the tissue in which they reside or the organism as a

whole? To these scientists, the mitochondrial free radical theory of aging

seemed dead in the water.

This was where the field sat in the mid-1990s, when I first became

aware of the unsatisfactory state of aging science and decided to try to do

something to change the situation. When I saw the confused state of the

mitochondrial free radical theory of aging, I felt that the field looked ripe

for a new synthesis. On the one hand the evidence supporting the existence

of a central role for mitochondrial free radicals in aging seemed strong; on

the other hand, the standard vicious cycle theories simply could not be rec

onciled with the emerging results. It was into this fray that I stepped with

my first formal scientific papers in 1997 9 and 1998, 1 0 and where I have

made my most widely acknowledged contributions to biogerontology. My

key insights were, firstly, an explanation of how aging cells accumulate mi

tochondria that share one mutation in common instead of the random set

predicted by the vicious circle theory, and secondly, an explanation of how

only a small number of cells taken over by such mutant mitochondria could

drive aging in the body as a whole. Let's walk through these ideas one at a

time.

SOS: Survival of the Slowest

The vicious cycle theory had assumed that each mitochondrion would

slowly accumulate minor, random mutations over the course of its lifetime.

The fact that, in those cells where there were mutant mitochondria, all the

mutants shared the same mutation—and that the mutants had completely re

p l a c e d all healthy mitochondria in the cell—proved that assumption wrong.

The only reasonable alternative seemed to be "clonal expansion": the

idea that a single mitochondrion had originally gone bad, and that its prog

eny had slowly taken over the entire cell. Remember, mitochondria repro

duce themselves by splitting themselves in half, much like amoebae: the

original mitochondrion makes a copy of its DNA, and then forms two iden

tical genetic "clones" of itself. This means that each clone will contain ex

act copies of any mutations present in the original organelle. So it seemed

inescapable that the strange mitochondrial monocultures found in the all-

mutant cells were the result of one mitochondrion initially acquiring a mu-


tation, passing it on to its offspring, and then having its lineage somehow

outcompete all of its neighbors until it eventually becomes the only game in

town.

However, the idea that mitochondria with mutated DNA could some

how win a battle for dominance within the cell was itself a bit of a paradox.

After all, these mitochondria are defective, with one or more enormous

chunks blasted out of their DNA by free radicals or replication errors. While

it's true that once in a blue moon a mutation turns out to be beneficial—this

is, after all, what allows evolution to happen—it's supremely unlikely that it

would happen over and over again, such that random mutations occurring in

mitochondria in widely separated cells would turn out to be so beneficial to

the mitochondrion as to give it a Darwinian "fitness advantage" over its fel

lows. And indeed, the mutations in question were known to be deleterious:

they completely knock out the mitochondrion's ability to perform oxidative

phosphorylation, and thus turn off the great majority of their contribution to

the cellular ATP supply.

The "clonal expansion" explanation was also hard to reconcile with the

fact that many different mutations can cause a specific mitochondrial line

age to replace all other alternative lineages in the cell. That is: while the mu

tant mitochondria in a given cell all contain the same, specific mutation, a

second such cell often contains mitochondria that all harbor a completely

distinct mutation from the one that was found in the first. So it wasn't that

there is a single, specific mutation that gives the mutants their selective ad

vantage over their neighbors: numerous mutations, independently arising

in single mitochondria within widely separated cells, confer the same com

petitive edge. Was it really likely, I asked myself, that there were this many

advantageous, yet unrelated, mutations to be had?

Yet, these various mutations do have one thing in common. They aren't

mild mutations, damaging just one protein: all of them are of a type that

prevent the synthesis of all thirteen of the proteins that the mitochondrial

DNA encodes. This shared property, I felt, might be the key to how they

managed to take over the cell.

I set myself to thinking what would distinguish such mitochondria from

their healthy counterparts. They would not generate nearly so much ATP, of

course: only the small amount of cellular energy that gets p r o d u c e d in the ini

tial stages of extracting chemical energy from food, which was a fraction of

the total that a functioning oxidative phosphorylation system could churn

out. This would be unhealthy for the cell, certainly, but I realized that it

would have little negative impact on the mitochondrion itself, which normally


exported nearly all of the ATP that it p r o d u c e d anyway. So, while I couldn't

see how this r e d u c e d energy output could explain the selective advantage en

joyed by the mutants, I saw that—contrary to what one might initially

think—-it really wasn't a direct disadvantage relative to other mitochondria in

the cell that might hinder them from rising to dominance in the host.

The other thing that would set mitochondria with no oxidative phospho

rylation capacity apart from other mitochondria in a cell seemed more likely

to be advantageous: such mitochondria would no longer be producing free

radicals. Remember that mitochondrial produce free radicals when electrons

leak out of the regulated channels through which they pump protons into the

"reservoir" that drives the "turbines" of the mitochondrial inner membrane.

If you aren't feeding electrons into the pump system because the system itself

is missing, then clearly there will be no leakage—and no free radicals.

Not having to deal with constant free radical vandalism sounded like it

might be good for the mitochondrion—but it was not clear exactly how it

might lead to an actual competitive advantage vis-a-vis the healthy mito

chondria with which it was surrounded. True, its DNA would stop being

bombarded—but of course, by this time it would already be suffering from

a gaping hole in its DNA.

It was also obvious that the mitochondrion's inner membrane would no

longer suffer free radical damage—but again, it didn't seem that this would

matter in aging, since mitochondria are constantly having their membranes

torn down and r e p l a c e d anyway, either during replication or at the end of

their brief individual lives, when mitochondria with defective membranes

are sent off to the cellular "incinerator" in any case.

Now hang on a minute, I thought.

Like other researchers who had puzzled over this question, I'd been

trying to imagine some improvement to the mitochondria's function con

ferred by the mutation—the equivalent, in the microscopic evolutionary

struggle, to sharper teeth, faster running, or greater fecundity. But what if,

instead, the important thing about the mutation was not that it made its

carriers "better," but that it prevented them from being destroyed?

Recycling Cellular Trash

There's still a lot of work to be done to explain what exactly causes mito

chondria to be sent to the cellular garbage disposal system. Still, even as

early as Alex Comfort's criticism of the original mitochondrial free radical


theory of aging, it was widely believed that there was some selective process

that specifically targeted old, damaged organelles for destruction. This

could not be taken for granted, however. It was long believed that some

components of the cell are turned over by an ongoing process of random

recycling, in which the lysosome (strictly, a special sort of pre-lysosome

called an autophagosome or autophagic vacuole) simply lumbers about the

cell, swallowing a given number of various cellular constituents at random

each day, so that everything is ultimately turned over sooner or later.

It is now widely accepted that this isn't the way the lysosome works: the

engulfment of proteins and other cellular components is known to be a

highly directed process. In part, this is simply a matter of good use of scarce

resources. Imagine if, in order to ensure that old, decaying vehicles were

taken off the road (to improve the nation's overall air quality and greenhouse

gas emissions, eliminate the eyesore of old cars rusting on blocks, and bring

down the price of recycled steel), the government were to send its agents

wandering aimlessly through economically depressed neighborhoods to ran

domly select cars to be sent off to the scrap heap. Such a program would

achieve some of its goals, but it would hit too many fully functional vehicles

to make it viable, even setting aside the question of individual property rights.

But in some cases there is an even more powerful reason than mere ef

ficiency to be sure that specific organelles get sent to the scrap heap. Some

cellular components can become actively toxic to the cell if they aren't

quickly degraded once they've outlived their usefulness. Like the en

chanted broom in Fantasia that continues to fill the vat in the sorcerer's hall

with water until it overflows and floods the room, many proteins and or

ganelles are only useful for a limited period; when their job is done, they

must be "put away," and in the cell, this means torn apart for recycling. For

instance, producing a pro-inflammatory enzyme can be critical to mobiliz

ing an immune reaction against an invading pathogen, but leaving that en

zyme to keep generating inflammation after the invader has been defeated

would lead to a destructive, chronic inflammatory state with effects similar

to those of autoimmune diseases like rheumatoid arthritis or lupus.

It then occurred to me that there were very good reasons for the cell to

take care that its mitochondria were destroyed when their membranes had

suffered free radical damage. Recall that the inner mitochondrial mem

brane acts as a "dam" to hold back the reservoir of protons that powers the

energy-generating turbine of Complex V. Holes in that membrane would

be "leaks" in the dam, depleting the reservoir as ions simply seeped

through the holes without generating ATP. Evidence to confirm this basic


scenario, in the form of leaks created from damaged membrane molecules,

had actually been uncovered as early as the 1970s.11

This would make the "leaky" mitochondrion a serious drain on scarce

resources, as the electron chain would continue to consume energy from

food in a furious, futile attempt to refill the reservoir. Food-derived elec

trons would continue to be fed into the chain, which would use them to

keep pumping protons across the membrane, but these ions would leak

back across as fast as they were pumped "uphill," without building up the

electrochemical reservoir needed to create usable energy for the cell. This

would drain the cell of energy, turning nutrients not into ATP but instead

into nothing more useful than heat.

Moreover, the damage to the inner membrane might also allow many

of the smaller proteins of the mitochondrial inner space to be released out

of the mitochondrion and into the main body of the cell. If they continued

to be active, these components could well be toxic to the cell when released

from the controlled environment of the mitochondrion.

It would make sense, then, for the cell to have a system in place that

would ensure that mitochondria are hauled off to the lysosome for destruc

tion when their membranes become damaged by their own wastes. This pre

diction seems to have been fulfilled with the recent discovery of a specific

targeting protein that "tags" yeast mitochondria for lysosomal pickup. 1 2 We

still don't know for sure what makes the cell decide which mitochondria to

"tag," but it has now been shown that the formation of holes in the mito

chondrial membrane does send a signal that increases the rate at which these

organelles get sent to the scrapyard. 1 3

I had no doubt that this was all to the good: I'm all for the removal of

defective and potentially toxic components from the cell, and as usual na

ture has evolved an ingenious way to make sure that it happens. But I saw

that, ironically, large deletions in the mitochondrial DNA would actually al

low them to escape from the very mechanism that cells use to ensure that

damaged mitochondria get slated for destruction. When mitochondria suf

fer the mutations that have been shown to accumulate with aging, they im

mediately cease performing oxidative phosphorylation (OXPHOS)—and

with it, generating the resultant free radical waste. But r e d u c e d free radical

production, in turn, should lead to less free radical damage to their mem

branes. Don't forget that the prevailing vicious cycle theory proposed that

mitochondrial mutations proliferate by causing their host mitochondria to

make more free radicals than nonmutant mitochondria do. That, I saw, was

where the proponents of the vicious cycle theory had gone wrong.


Hiding Behind Clean Membranes

Having advanced this far, I immediately saw how the mutants gained their

advantage over their healthy counterparts. Even perfectly functional mito

chondria constantly produce a steady, low-level stream of free radicals,

leading to membrane damage. Every few weeks, this damage builds up to a

level at which the mitochondria are consigned to the rubbish tip, and then

the cell sends out a signal for a new round of mitochondrial reproduction to

replace the decommissioned "power plants."

But this process only weeds out mitochondria with damaged

membranes—which will overwhelmingly be power plants whose DNA is still

healthy enough to allow for the very electron transport that leads to the free

radical damage to their membranes in the first place. Mitochondria with in

tact membranes, but damaged DNA, would not show outward signs of their

internal injuries, and so would be passed over by the Angel of Death.

After a certain number of damaged mitochondria have been hauled off

to the lysosome, the cell will send out the signal for mitochondria to repli

cate. Some or all of the remaining mitochondria—the genetically healthy

and the mutants alike—will reproduce themselves, and because those mito

chondria that bear large DNA deletions will almost always have survived

the purge of outwardly damaged power plants, they will enjoy the opportu

nity to reproduce. But many of the membrane-damaged—but genetically

intact!—mitochondria will already have been removed before replicating

themselves. This will give the mutants a selective advantage over the non-

mutants: every time replication happens, more and more of them will have

survived a cull that has sent many of their genetically healthy competitors

to the garbage disposal unit.

This is exactly how evolution works in organisms, of course. Animals

that are slower runners, or less able to find food, or have poorer eyesight

are more vulnerable to death from predators, exposure, or disease, which

prevents them from successfully reproducing and passing on their genes.

Meanwhile, a disproportionately high number of better-adapted organisms

get the chance to breed, leaving behind progeny that carry their genetic

legacy into the future. Over time, the genes that are best adapted to the spe

cific threats in their environment come to dominate in the population.

In the cell, the threat to mitochondrial survival is the lysosome—a

"predator," which is supposed to ensure that only mitochondria fit to safely

support cellular energy production survive. What the mutant mitochondria

evolve (yes, evolve) is, in effect, camouflage that masks them from the eagle


eye of this predator. Thanks to their undamaged membranes, these highly

dysfunctional mitochondria appear healthy to the cellular surveillance sys

tem. Like the proverbial pharisees, their outsides are clean—but inwardly,

they are full of ravening and wickedness.

I concluded that this "camouflaged mutant" concept provided the first

consistent, detailed explanation for the takeover of cells by defective mito

chondria. I named it "Survival of the Slowest" (SOS), because it postulates

that the quiescent ("slow") mitochondria enjoy a fitness advantage in the

Darwinian fight for survival in the cellular jungle. See Figure 3.

But now, having explained how a small number of cells become a

monoculture of defective mitochondria, there remained a question which

might be thought to be more important—namely, how does that tiny frac

tion of the body's cells drive aging across the entire body? It wasn't long be

fore I had a good explanation for that, too.

The "Reductive Hotspot Hypothesis"

The old vicious cycle models didn't need to invoke any additional mecha

nism to explain how mitochondrial mutation could contribute to aging, be

cause they assumed that there would be an accumulation of increasingly

defective mitochondria in lots of cells with age. As more and more of their

mitochondria randomly went on the blitz, the cells would suffer more and

more oxidative hits, and be more and more starved for ATP, as the power

plants' efficiency sank with every new defect. It was a nice, common-sense

explanation for the role of mutant mitochondria in the aging of the body.

But, as we've seen, it was also clearly wrong. Most cells in the body sim

ply do not accumulate mutant mitochondria as we age: at most, about 1 per

cent of all of the trillions of cells in the body do so. Most cells and tissues

suffer no decline in production or availability of ATP, and far from increasing

free radical production, most of the mutant mitochondria that accumulate in

the body produce no free radicals at all, because their radical-generating elec

tron transport chains are simply absent.

It was hard to see how so few cells, containing mitochondrial mutants

that were not harming nearby cells in any obvious way, could possibly be

driving aging in the body. In fact, these findings were enough to make plenty

of biogerontologists talk about the death of the mitochondrial free radical

theory of aging. Yet, as we briefly discussed earlier in this chapter, the cir

cumstantial evidence that mitochondrial mutations somehow contribute to


Figure 3. The "Survival of the Slowest" model for mitochondrial mutation accumulation, (a) The proposed normal mode of turnover and renewal of non-mutant mitochondria; spots denote membrane damage. (b) The clonal expansion of mutations (denoted by X) resulting from low free radical damage to membranes and slow lysosomal destruction.

aging is too strong to dismiss. To reconcile the two sets of data would re

quire a truly novel solution to the puzzle.

I saw that any refined version of the mitochondrial free radical theory

of aging would have to do two closely related things. First, since so few cells

are taken over by these burned-out power plants, it would have to show

that cells harboring mutant mitochondria somehow spread toxicity beyond

their own borders. And second, it would have to explain the nature of that


toxicity, since the usual suspect—free radicals—appeared to have been

ruled out by the fact that the mitochondria in these cells would have their

normal free radical production turned off at the source.

I began by trying to work out just what cells that had been taken over

by mutant mitochondria were doing to survive in the first place. What were

they using as an energy source? Not only were these mitochondria unable

to perform the oxidative phosphorylation that provides their host cells with

the great majority of their ATP, but it was not at all obvious how they could

produce any cellular energy at all.

Upstream of a Blocked Dam

In normal cells, the initial metabolism of glucose from food is performed in

the main body of the cell through a chemical process called glycolysis. Gly

colysis generates a small amount of ATP, a breakdown product called pyru

vate, and some electrons which can drive oxidative phosphorylation in the

mitochondria. To shuttle electrons into the mitochondria for this purpose,

they are loaded onto a carrier molecule called NAD +. The charged-up form

of NAD + is called NADH.

The pyruvate formed during glycolysis is also delivered into the mito

chondria, where it is further broken down into another intermediate called

acetyl CoA. This process releases some more electrons, which are again har

vested for use in electron transport by "charging" NAD + into NADH.

Acetyl CoA is then used as the raw material for a complex series of chemi

cal reactions called the tricarboxylic acid (TCA) cycle (also called the Krebs

cycle or citric acid cycle), which liberates many times more electrons (again

leading to creation of NADH) than has been created in previous steps.

Finally, all of the NADH charged up via all these processes—glycolysis,

the breakdown of pyruvate into acetyl CoA, and the TCA cycle—is deliv

ered to the electron transport chain, which uses this electron payload to

generate the proton "reservoir" that drives the generation of nearly all the

cell's energy.

This was well-understood biochemistry, taught in its simple form to

students in middle-school science classes. But it's all predicated on being

able to feed these electrons into the electron transport chain machinery. So,

I asked myself, what would happen when that machinery was shut down, as

it is in mitochondrially mutant cells?

It seemed to me that the whole process might grind to a halt. Every


step along the way—from glycolysis to the TCA cycle—loads electrons

onto waiting NAD + "fuel tankers" for delivery to the electron transport

chain. There is, of course, only a limited supply of NAD + "carriers" avail

able to be charged up into NADH, but normally that isn't a big deal: there

are always plenty of these carriers available, because NADH is recycled

back into NAD + when it releases its electron cargo to the electron transport

machinery in the mitochondria.

But with that natural destination shut off, there is no obvious way for

NADH to relieve itself of its burden of electrons. (Similarly, you can imag

ine how, if all the refineries on Earth were suddenly decommissioned, the

taps on the world's oil wells would quickly need to be turned off. With

nowhere to deliver their oil for processing, fuel tankers could only be filled

once before their capacity would be taken out of circulation, and continu

ing to pump oil would lead to a logistical nightmare.) And since every step

of the process—glycolysis, intermediate metabolism of pyruvate into acetyl

CoA, and the TCA cycle—needs NAD + to proceed, a lack of NAD + would

be expected, at first glance, to lead to the deactivation of the entire process,

leaving no mechanism for the cell to produce even the small quantities of

ATP energy that result from these early processing steps.

In fact, I could see how mitochondrially mutant cells might be even

worse off than this. NAD + is required for a wide range of cellular functions

unrelated to energy production—and each time these functions utilize

NAD +, they not only reduce the pool of available NAD + , they also convert

it to yet more NADH, further upsetting the cell's metabolic balance. In

fact, some researchers believe that many of the complications of diabetes

are caused by an excess of NADH and a lack of NAD + , leading to disrup

tion of these various metabolic processes (although the imbalance of NAD +

and NADH in diabetics has different causes than the loss of OXPHOS

capacity).

Despite all this, however, cells that have been taken over by mutant mi

tochondria do survive, as is shown by their gradual accumulation with ag

ing. So they have to be getting ATP from somewhere. At the time I was

exploring this matter, the general presumption in the field was that these

cells could survive by shutting down the TCA cycle and relying entirely on

glycolysis for energy production. This is what happens in muscle cells as a

brief stopgap during intense anaerobic exercise, when the cell is working so

hard that it uses up all of the available oxygen and can't keep oxidative

phosphorylation going. Glycolysis would provide the cell with a small but

just adequate amount of ATP, and this school of thought suggested that the


cell could deal with the resulting small excess of NADH through a bio

chemical process that converts pyruvate into lactic acid—the biochemical

origin of the famous "burn" that weightlifters suffer during the very last

possible rep in their set.

But I realized that this theory didn't match the evidence. For one

thing, the expected rise in lactic acid didn't seem to happen. And even

more bizarrely, rather than a shutdown of TCA activity (as one would ex

pect because of the lack of the required free NAD +), enzyme studies had

strongly suggested that mitochondrially mutant cells have hyperactive TCA

cycles. So, I wondered, how do they keep this seemingly unsustainable

process going?

Learning from the Great Mr. Nobody

A big step toward understanding this phenomenon was achieved with the

creation of so-called p0 ("rho-zero") cells, whose mitochondria are com

pletely lacking in DNA. This condition renders cells functionally very simi

lar to cells that have been overtaken by mutant mitochondria, because the

deletion mutations found in these mitochondria actually shut down the

ability to turn any DNA instructions into functioning proteins. If your

DNA can't be decoded into usable blueprints, it might as well not be there,

like instructions on how to build a bridge that are written in a language you

don't understand. So having these DNA deletions puts mitochondria in just

the same condition as having no mitochondrial DNA at all.

One of the first things that scientists working with p° cells discovered

was that they did, in fact, quickly die—unless their surrounding bath of

culture medium contained one of a few compounds which are not normally

present in the fluid that surrounds cells in the body. Intriguingly, however,

some of these compounds are unable to enter cells, which meant that what

ever it was that these compounds do to keep cultured p° cells alive, it must

be something that can be accomplished from outside the cell. This fact

made little sparks go off in my brain, because I was looking for a way to ex

plain how cells that had been overtaken by a clonal brigade of mutant mi

tochondria could export some kind of toxicity outside themselves to the

body at large. Might these compounds rescue p0 cells by unburdening them

of this same toxic material?

And might this toxic material be none other than . . . e l e c t r o n s ?

I immediately drew a connection between the predicted excess of


NADH in cells that could not perform oxidative phosphorylation, and the

dependence of p° cells on the presence of the "detoxifying" compounds in

their medium. What the mitochondrially mutant cell needed to do was to

dump electrons, so as to recover some NAD+—and the "rescue" compounds

for p° cells were all electron acceptors, and they worked even if they were

kept outside the cell's boundaries. My hypothesis: Mitochondrially mutant

cells prevent a crippling backlog of unused electrons by exporting them

out of the cell, via a mechanism similar to that which is essential to the sur

vival of p0 cells in culture—and this export somehow spreads toxicity to the

rest of the organism.

The Safety Valve

To turn this idea into a reformulation of the mitochondrial free radical ag

ing theory, I needed clear answers to three questions. First, how were these

cells delivering electrons to acceptors that were located outside their own

membranes? Second, since the electron acceptors used in the p° culture

studies are normally not found in bodily fluids (or not at adequate concen

trations), what electron acceptors are available to do the same job for mito

chondrially mutant cells in the body? And third, could these processes

provide an explanation for these cells' systematic spread of toxicity

throughout the body, as seemed required in order to accept that they might

play a significant role in aging?

The first question turned out to have been answered already. For de

cades, scientists had known of the existence of an electron-exporting fea

ture located at the cell membrane that we today call the Plasma Membrane

Redox System (PMRS). While little was understood about its actual pur

pose in the body, its basic function was well established: it was known to

accept electrons from NADH inside cells and to transport them out of the

cell, thereby recycling the NADH to NAD +. This export allows even nor

mal, healthy cells to have better control over the balance of chemically oxi

dizing and reducing factors within their boundaries, and to keep tighter

control over the availability of NAD + and NADH for essential cellular bio

chemistry. In other words, it does exactly what mitochondrially mutant

cells would need to be able to do in order survive.

And the PMRS turned out to be an almost impeccable candidate for

the job. PMRS researcher Dr. Alfons Lawen, of Monash University in Aus

tralia, had by this time already shown (with no thought of its application to


aging, mind you) not only that the PMRS is able to deliver electrons to the

same membrane-impermeant electron acceptors that allow p° cells to sur

vive, but that PMRS activity is required for the survival of these cells. This

proved both that the export of electrons is a requirement for cell survival,

and that the PMRS is the dock that sets them loose into the ocean of sur

rounding bodily fluids.

The ability of mitochondrially mutant cells to recycle NADH back to

NAD + would allow them to carry out their normal cellular processes, and

without becoming so burdened with extra electrons as to create an internal

environment in which other critical cellular chemistry becomes impossible.

Moreover, I realized, this is a plausible explanation for the fact that these

cells have an unusually active TCA cycle. With oxidative phosphorylation

shut down, putting the TCA cycle into overdrive would allow the cell to

double its production of precious ATP from sugars (and to do many other

metabolic jobs in which the TCA cycle participates). The PMRS would

make this possible, by recycling the greatly increased amounts of NADH

that would be created and thereby providing the cell with the extra NAD +

required to keep the process going.

But the drastic increase in PMRS activity required to make the increased

TCA activity sustainable would make the surfaces of mitochondrially mu

tant cells positively bristle with electrons undergoing export, forming a

hotspot of electrically "reducing" pressure (i.e., an unstable excess of elec

trons). The next question, therefore, was onto what molecules the PMRS

was unloading the electron surfeit. None of the electron acceptors being

used to keep p° cells alive in culture existed in adequate concentrations in

the body to accomplish the task, so something else had to be performing

this essential role. For example, some of the burden might be taken up by

dehydroascorbate, the waste product of vitamin C that is created after it is

used in quenching free radicals, but there wasn't enough of that to deal

with the powerful "reductive hotspot" created by these cells.

At this point, an attractive candidate that could tie the story together

flashed into my mind: our old two-faced friend, oxygen.

Don' t Throw Your Junk in My Backyard, My Backyard . . .

Oxygen, of course, can and does absorb surplus electrons in its environ

ment. As we discussed above, this is exactly how mitochondria generate

free radicals during oxidative phosphorylation, as "fumbled" electrons


slipping out of the electron transport chain are taken up by the oxygen dis

solved in the surrounding fluid. And oxygen is the only such molecule in

the body's bathing fluids that is present in sufficient quantity to be able to

sponge up the huge electron leak that mitochondrially mutant cells would

be predicted to generate.

This uptake of electrons by oxygen could, in an ideal world, be safe: the

PMRS might load four electrons onto each oxygen molecule, turning it into

water, just as the electron transport chain does with electrons that it doesn't

"fumble." But it was eminently possible that the PMRS would fumble some

electrons—maybe quite a lot of them. If so, it would generate large amounts

of superoxide radicals at the surface of mitochondrially mutant cells. The

consequences of this would clearly be bad. But actually, maybe not so bad:

one might think that the negative effects would mostly be confined to the

immediate locality. Like nearly all free radicals, superoxide is highly reactive,

and therefore short-lived. Either it would be dealt with by local antioxi

dants, or else it would attack the first thing with which it came into contact

(a neighboring cell's membrane, for instance)—but its aggressiveness would

be quenched in the process. Superoxide certainly couldn't remain a free

radical for long enough to reach the far corners of the body, as the implica

tions of the mitochondrial free radical theory required.

But what if, instead of attacking the components of a cell's immediate

neighbors, superoxide generated by the PMRS were to damage some other

molecule that was then stable enough to be carried throughout the body?

There was an obvious suspect: serum cholesterol, especially the LDL

("bad") particles—low-density lipoproteins, to give them their full name—

that deliver their cholesterol payload to cells all over the body.

Oxidized (and otherwise modified) cholesterol was already known to

exist in the body, and everyone now accepts that it's the main culprit be

hind atherosclerosis (a subject to which we'll return in Chapter 7). It was

quite plausible, I realized, that superoxide originating at the surface of mi

tochondrially mutant cells could be oxidizing LDL as it passed by, not only

because LDL is ubiquitous and therefore an easy target, but also because

the presence of loosely bound reactive metals such as iron ions would mul

tiply superoxide's potential virulence. One might think that the presence of

antioxidants—such as the vitamin E that's dissolved in LDL—would pre

vent this from happening, but researchers had already discovered that it

didn't. Not only is oxidized LDL found routinely in the body, but studies

using the most accurate available tests of lipid peroxidation had shown that

vitamin E supplements were unable to reduce the oxidation of fats in


healthy people's bodies. 1 4 In fact, the lack of antioxidant partners in the in

accessible core of the LDL particle means that when it is subjected to any

thing more intense than the most trivial free radical challenge, the particle's

vitamin E can actually accelerate free radicals' spread to its center through

a phenomenon called "tocopherol-mediated peroxidation." 1 5 (Tocopherol

is the technical name for vitamin E.)

I saw the light at the end of the logical tunnel now. The oxidation of

LDL would provide a very plausible mechanism to explain the ability of

mitochondrially mutant cells to spread oxidative stress throughout the ag

ing organism. Despite its ability to promote atherosclerosis when present in

excessive amounts in the blood, LDL cholesterol serves an essential func

tion in the body. Cells need cholesterol for the manufacture of their mem

branes, and LDL is the body's cholesterol delivery service, taking it from

the liver and gut (where it is either manufactured or absorbed from the

diet) out to the cells that need it.

But if its cholesterol consignment became oxidized by mitochondrially

mutant cells along the way, LDL would become a deadly Trojan horse, de

livering a toxic payload to whichever cells absorbs its cargo of damaged cho

lesterol. This would spread free radical damage into the incorporating cell,

as the radicalized fats propagated their toxicity through the well-established

chemical reactions that underlie the rancidity of fats. As more and more cells

were taken over by mutant mitochondria with age, more and more cells

would accidentally swallow oxidized LDL, and oxidative stress would grad

ually rise systemically across the entire body. See Figure 4.

The New Mitochondrial Free Radical Theory of Aging

I walked myself through the entire scenario again and again, and gradually

satisfied myself that I had indeed developed a complete, detailed, and con

sistent scenario to explain the link between mitochondrial free radicals and

the increase in oxidative stress throughout the body with aging. This model

answered all of my key questions and resolved all of the apparent para

doxes that had led so many of my colleagues to abandon the mitochondrial

free radical theory of aging entirely. Mitochondrial free radicals cause dele

tions in the DNA. These mutant mitochondria are unable to perform ox

idative phosphorylation, drastically reducing their production of both ATP

and free radicals. Because they are not constantly bombarding their own

membranes with free radicals, the cell's lysosomal apparatus will not recog-


Mitochondrially mutant

cell (no aerobic respiration)

creates reductive stress

at its surface.

AEA = Antioxidant electron receptor.

AEAr = Reduced AEA.

Extracellular defences are

many and various, but not

100% effective.

Mitochondrially healthy cell

(aerobically active) may

suffer damage to lysosomes

and hence more general stress.

Figure 4. The "reductive hotspot hypothesis" for amplification of the toxicity of rare mitochondrially mutant cells.

nize them as defective and they will gradually drive out their healthy neigh

bors. (This was the maladaptive evolutionary process that I had already, a

year previously, termed "Survival of the Slowest.")

To continue producing the ATP and other metabolites their host cells

need for survival, these mitochondria must maintain the activity of their

TCA cycle—but this, combined with other cellular processes in the absence

of oxidative phosphorylation, will quickly deplete the cell of needed NAD +

carriers unless a way is found to relieve them of their electron burden. This

is accomplished via the "safety valve" for excess electrons located at the cell

membrane—the Plasma Membrane Redox System (PMRS).

The snarling buzz of electrons congregating at these cells' outer sur

faces turns them into "reductive hotspots," generating a steady stream of


superoxide free radicals. These radicals contaminate passing LDL particles,

which then spread to cells far away in the body, driving a systemic rise in ox

idative stress throughout the body with age. With oxidative stress comes

damaged proteins, lipids, and DNA, as well as inflammation, disrupted cellu

lar metabolism, and maladaptive gene expression. This could certainly be a

central driver of biological aging.

The whole theory is unattractively elaborate, as you'll have gathered, and

as I immediately appreciated—but as far as I can tell, it's the only hypothesis

that can accommodate all of the data. I published the twin arms of the theory

in rapid succession in the late 1990s, and a more detailed presentation of the

integrated theory was accepted as my Ph.D. thesis for Cambridge and pub

lished in the Landes Bioscience "Molecular Biology Intelligence Unit" se

ries. 1 6 In the ensuing years the theory has enjoyed widespread appreciation

and citation in the scientific literature. Unfortunately, despite this fact, both

the popular press and many biogerontologists1 7 continue to cite the long-

disproven vicious cycle theories either to support or to refute the role of mi

tochondria in aging, instead of seriously grappling with this detailed

mechanistic account.

So now you know, in minute detail, my interpretation of why mito

chondrial mutations are probably a major contributor to mammalian aging,

and therefore why they are included as a category of "damage" in the defi

nition of SENS. The question, then, is what to do about the toxic effects of

mitochondrially mutant cells. The solution to this problem is the subject of

the next chapter.

G e t t i n g Off t h e G r i d

There are good reasons to believe that most present attempts to

modify metabolism to produce less damage to mitochondria

(and thereby to the body at large) are a poor use of resources.

Fortunately, a better path forward exists, promising far greater

results for the same application of time and money. It seems

possible and plausible to prevent damage to mitochondria from

harming us as we age—and scientists are already working on

many options for the first steps of this process.

In the previous chapter, I explained in excruciating detail my

views about the complex mechanisms whereby mitochondrial DNA dele

tions may act as a major engine of aging. I must now tell you that in a very

real sense, it simply does not matter if that hypothesis is correct or not.

This point applies equally strongly to the other SENS interventions,

and it is so central to the engineer's approach to anti-aging medicine—and

so enormously counterintuitive—that I must beg your indulgence if you

find me to be repeating it too often. We must all keep it in the forefront of

our minds when thinking about these problems. If our purpose were

simply to understand aging, then teasing apart the specific pathways that

lead to the accumulation of age damage would indeed be absolutely imper

ative. But that is not our purpose. Our purpose is to put an end to aging's

consequences: the daily descent into decrepitude, and subsequent deaths,

of tens of thousands of people.

6


Aging is a deadly pandemic disease, and I believe that our understand

ing of its mechanisms, while still highly imperfect, is now good enough that

we are in a position to intervene in it. We need only to identify the nature

of the damage itself—the accumulating lesions that are the source of age-

related loss of functionality in the organism—and then either to reverse

that damage, or to eliminate its threat to our health and life expectancy.

This goal should become the central focus of biogerontological work, and

the major target of biomedical funding generally.

The problem of mutant mitochondria is a case in point. Mitochondrial

DNA mutations are a form of molecular disorder that distinguishes the bi

ologically young from the biologically old, and there is powerful evidence

that they are deleterious. 1 So, whether mutant mitochondria take over their

host cells via "Survival of the Slowest" or through some other mechanism,

and whether these cells exert their toxic effects on the rest of the body by

way of the export of electrons through the PMRS or via a completely unre

lated process, the nature of the task at hand is ultimately the same. Our

therapeutic goal is clear: either to fix the mutations themselves, or to make

them functionally irrelevant. How to achieve that goal is the subject of this

chapter.

Before laying out my proposals to accomplish this goal, however, I

must first spell out why the appealing-sounding solutions that many

biogerontologists would propose are probably wastes of time and scarce

resources.

You Can' t Stop a Moving Train (Safely!)

I termed the "over-preventative" approach to combating aging the "geron

tology" approach because biogerontologists predominently favor it. By and

large, when my colleagues think seriously about actually doing something

about aging rather than just refining their understanding of it, their first in

stinct is to find some way to make metabolism run more cleanly. After all, ag

ing is the result of the accumulation of the deleterious by-products of our

metabolic processes; surely, the thinking goes, if we could just tweak or

dampen down those processes a little bit, we could reduce the exposure of

the organism to metabolism's reactive by-products, reduce the rate at which

our cells and tissues accumulate microscopic damage over time, and thus

slow down the gradual decay of our bodies into age-related frailty and accel

erating vulnerability to death.

G E T T I N G O F F T H E G R I D 7 9

This approach has a strong intuitive appeal, re inforced by the continu

ous stream of encouragement from supplement vendors and public health

authorities alike. We are constantly urged to clean up our lifestyles and

practice preventive medicine: surely, we think, it makes more sense to put

one's energies into attempting to interfere with the causes of aging and age-

related diseases than to try to undo an established molecular mess. But, as

we saw in Chapter 3, the causes of aging lie in the fundamental chemistry of

life, and our capacity to interfere beneficially with that chemistry is limited

by what the organism's underlying biology will accommodate.

I gave examples of this general principle in Chapter 3, but let's now

look at the more concrete case of intervention into the problem of mito

chondrial mutations. The obvious, old-school approach would be to try to

reduce the formation of mutant mitochondrial DNA by cutting back on the

bombardment of the mitochondrial DNA by free radicals. Just such a trick

has been pulled off with some success in mice 2 by giving them a copy of the

gene for the antioxidant enzyme catalase, specially targeted to their mito

chondria. Catalase breaks down the free radical-like molecule hydrogen

peroxide, turning it into harmless water before it can become more vicious

and do serious molecular damage. Animals that received the targeted cata

lase gene enjoyed a fifty-fold jump in the activity of the enzyme within their

mitochondria, preventing a great deal of mitochondrial DNA damage—

including some of the mutations that initiate the whole destructive process

of decay that I described in the last chapter.

Compared to the repeated, abject failures of dietary antioxidants to ex

tend lifespan, or the ambiguous 3 , 4 , 5 or negative 6 results of previous attempts

to hold back the free radical onslaught in mice using genetic manipulations,

these results are quite impressive. Mice given mitochondrially-targeted cata

lase gained a 20 percent extension not only of average, but of maximum

lifespan—the gold standard for data relevant to aging. And while no detailed

analysis of the level of age-related pathology in these animals has been pub

lished, we do know that they suffer less age-related heart degeneration and

fewer cataracts.

This being so, why should we not vigorously pursue the development

of a targeted boost in mitochondrial catalase for h u m a n s ? Well, in part this

goes back to the testability (and, thereafter, the possibility of full clinical

development) of this intervention. It suffers the same sorts of weaknesses

on these fronts that characterize all "preventive" anti-aging medicines, as

outlined in Chapter 3. Firstly, because there is no short-term disease against

which extra catalase could be tested as a cure, regulatory bodies won't let


clinical trials be performed using it, and will never approve it for human

use; and secondly, the timescales required to prove its effectiveness against

aging make it too expensive and risky for venture capital to touch it. That

probably means that no amount of agitation by scientists or the public will

actually put mitochondrially targeted catalase into the hands of clinicians to

save people's youth, health, and lives: the interests of those with the power

to fund or halt development are aligned against moving forward.

But even if these structural hurdles did not exist, I would still conclude

that there are more fruitful soils into which to plow our limited resources

for dealing with mitochondrial mutations. Boosting these mice's catalase

supply reduces the incidence of mitochondrial mutations—but it doesn't

eliminate or obviate them. Thus, it slows, but cannot treat, the progressive

accumulation of this form of aging damage. I think we can do a lot better

than this. My evaluation of the evidence indicates that it is not worth di

verting our intellectual and financial capital into an intervention that might

yield a 20 percent increase in lifespan (making the average person in a de

veloped country live into his or her late nineties), because the same bricks,

boards, and brains could be put to work in the development of an interven

tion that would not prevent this damage from happening, but would instead

render it harmless. My analysis suggests that this intervention might, in turn,

not only slash the rate of aging damage primarily caused by other mecha

nisms in half, but—when combined with a panel of similar therapies—

would ultimately give us an indefinite youthful lifespan. More on that in

Chapter 14.

In fact, if we were to eliminate, one by one, the other forms of molecu

lar damage that cause us to wither and to die as we age, but were to "only"

slow down the incidence of mitochondrial mutations by the degree seen

in the mitochondrially targeted catalase mice, we might find ourselves

stranded one step away from a future that stretches out further than our

eyes can see. When a d v a n c e d glycation endproduct (AGE)-breaking drugs

reverse the gumming up of our structural proteins; when careful exploita

tion of the immune system clears out the extracellular junk that impedes

cellular function; and when dormant cells that cause the decay of our im

mune system itself have been removed; at that time, with all the other key

SENS platform interventions in our hands, we would still have mitochon

dria that are playing a game of Russian roulette with their DNA. However

much more slowly they may be spinning the chamber, they could still end

up being the weak link in a chain that could otherwise give us indefinite

youthful lifespan.


We could apply these same objections to any approach to anti-aging

biomedicine based on prevention of aging damage instead of genuine re

mediation. But there is a more specific objection to the "catalase solution."

Relying on an extra dose of catalase to deal with mitochondrial mutations

could actually become harmful in important ways in a person whose body

had already been cleared of—or rendered immune to—all of the other

identified aging damage.

Catalase cleans up hydrogen peroxide, which can be damaging when it is

the result of imperfections in oxidative phosphorylation—as most of it is. But

evolution is, over the long term, an extremely clever engineer, and has

learned ways of making the best of a bad job, harnessing hydrogen peroxide

for its own purposes. While randomly spewing the stuff out of the cellular

power plants does us no particular good, our cells also generate some hydro

gen peroxide on purpose, for use as a chemical signal that regulates every

thing from glucose metabolism to cellular growth and proliferation.7 In this

way, damping down the level of hydrogen peroxide in a cell—even using a

technique designed to focus on the mitochondria—might well be expected

to interfere with the functioning of our complex intracellular machinery.

One of the most dramatic examples of this potential problem is the

need for hydrogen peroxide to reach the mitochondria themselves as part

of the signaling cascade that triggers apoptosis, or "programmed cell

death." Apoptosis is important during embryonic development as part of a

"remodelling" process that rids the nascent organism of excess cells that

are only required during specific phases of its growth. But its main role in

the body is similar to the self-destruct mechanisms built into James Bond's

Aston Martin or the Starship Enterprise: to give your cells a way to destroy

themselves if they have been hijacked by "enemy forces" (viruses or cancer,

for example) before they can threaten the integrity of the organism as a

whole. When the cells of our immune system detect a hijacked cell, they

bind to its surface, flipping a switch that signals its mitochondria to "blow

their tops" and destroy it. Hydrogen peroxide is a player in that signaling

system, and studies have shown that antioxidants—including catalase—

can block the proper activation of this apoptotic program.

Thus, the massive boosting of mitochondrial catalase activity that is re

quired to give these animals their partial protection from mitochondrial

DNA damage has a dark side. And while it's clear that the net effect of this

boost is good for them—as ev idenced by their extended lives and r e d u c e d

age-related pathology—the overall balance of risks and benefits would in

all probability be totally thrown off in an organism in which all other types


of aging damage had been eliminated. In this otherwise rejuvenated body, a

chronic dysregulation of cell signaling pathways would be a high price to

pay for lower oxidative stress.

Finally, there is reason to think that the catalase boost given to these

mice—which was performed in the mice while they were still early embryos,

rather than in adult organisms—might not even work if done in adult or

ganisms. Catalase genes only expressed the enzyme in some cell types, not in

others, and the scientists who performed the study suggested that this might

have been the result of a form of evolutionary selection during their devel

opment in the womb. The idea is that the extra catalase might be beneficial

in some kinds of cells but harmful in others, and therefore those cells that

were expressing a lot of the enzyme would tend to die off if they were of a

type in which the extra catalase was deleterious. Meanwhile, other cells of

the same type that did not express the new gene would survive, replicate,

and come to dominate. But performing the same trick in mature organisms

would short-circuit this internal evolutionary process, supplying the new

gene to all cell types indiscriminately, so that the benefits of the catalase gene

therapy in some cell types might be outweighed by negative effects else

where. This would mean that people unfortunate enough to have already

been born would not be able to reap any benefit from such therapy—and no

proposal to insert the gene into healthy developing infants, let alone em

bryos, is going to get past a medical ethics board.

None of this should dishearten us; it should simply remind us of the

need to focus our efforts elsewhere. As I outlined in Chapter 4, I advocate a

fundamentally different approach to dealing with age-related molecular

damage. Instead of trying to "mess with metabolism" in ways that might

prevent aging damage such as mitochondrial DNA deletions, it is my con

tention that we need to focus on developing anti-aging biomedicine that can

repair or render harmless any mutations that may occur in mitochondrial

DNA. While most people—whether laypersons or professional scientists—

tend to assume that this must be far more difficult to achieve than a preven

tive strategy, there are in fact several promising techniques sitting on the

drawing board that require no biotechnology more advanced than that

which would already be required to put catalase into the mitochondria—

namely, gene therapy. This suggests that we could actually have either type

of intervention in the clinic at about the same time. In fact, it really tells us

that the remedial technologies should be able to reach people suffering ag

ing damage sooner than preventive ones, for the regulatory and pragmatic

reasons I outlined earlier.


The Best Bet: "Head for the Bomb Shelter!"

As I discussed in the last chapter, the main reason for mitochondrial DNA's

unusual vulnerability to oxidative damage is its location: being next door to

a leaking nuclear reactor (the mitochondrial electron transport chain) is a

sure way to increase your risk of mutations, whether you're a growing child

or a tiny biological machine. Metabolism clean-up approaches try to make

this reactor run more cleanly (so that it produces less damaging waste), or

to install "pollution control" equipment that would catch more of its by

products before they do any harm (the cellular equivalent of the "smoke

stack scrubbers" on coal-fired power plants). My preferred approach is

completely different: that we should put these mutations "beyond use" of

harm. This could be accomplished by putting backup copies of the genes

that are currently housed in the mitochondria in the safe haven of the cell's

nucleus, far from the constant bombardment of free radicals from the mi

tochondrion itself. This solution is called "allotopic expression" of the pro

teins these genes encode—i.e., expression from a different (Greek allo-)

place (topos).

Let's be clear about this. Allotopic expression would do absolutely noth

ing to prevent the native mitochondrial genes from suffering mutations: free

radicals would hit the vulnerable mitochondria just as often, and mutations

would occur at exactly the same rate, as they did before. But with a nuclear

backup copy of these genes, any such mutations would be rendered func

tionally irrelevant, because the cell would be able to keep producing the pro

teins that the knocked-out genes in the mitochondrion had previously

encoded. These mitochondria would thus enjoy functional proton-pumping,

electron-transporting proteins, and would therefore behave exactly like mito

chondria with intact DNA, just as if they had not suffered mutations in their

"local" DNA. Electrons would continue to flow into the electron transport

chain from NADH; protons would continue to be pumped; free radicals

would continue to leak out of the system at random. The concept is illus

trated in Figure 1.

Not only that: because such mitochondria would continue to damage

their mitochondrial membranes, the cellular "incinerator system" (the lyso

some) would be able to tell when they got old and haul them off for de

struction. Therefore, the Survival of the Slowest mechanism that leads

mutant mitochondria to take over their host cells would never take place,

nor would cells be f o r c e d to shift into the abnormal metabolic state that

cells with mutant mitochondrial DNA require in order to deal with an


Figure 1. The concept of allotopic expression to obviate mitochondrial mutations.

imbalance in their NADH-to-NAD+ ratio. Thus, despite the fact that these

cells contain mutations in their mitochondrial DNA, they would not be un

loading their excess electrons into LDL, would not spread oxidative stress

to the rest of the body, and would make no more contribution to the aging

of the organism as a whole than cells with perfectly intact mitochondrial

DNA.

"But," I hear you ask, "what if one of these backup genes is itself mu

tated? Won't we be facing the same catastrophe?" Fortunately, no! There

is, in fact, no real risk of a functionally meaningful failure of this backup

system occurring, even over the course of a lifespan that has been dramati

cally extended by a full panel of SENS anti-aging interventions.

To understand why this is so, let's look at what would be required for

such a failure to occur. First, in order for a cell with an allotopic copy of a

mitochondrial gene to slide into Survival of the Slowest, it would have to

have suffered mutations in both copies of the gene: the mitochondrial orig

inal and the duplicate copy that we would have p l a c e d in the nucleus.

This is less likely to happen than it may initially sound. It is already un

usual for DNA located in the mitochondria to suffer permanent damage

(remember that as things stand, less than 1 percent of cells are overtaken by

mutant mitochondria), and the odds of a backup copy located in the nu

cleus being mutated are much lower. Aside from being better shielded from

free radicals because of its location (DNA housed in the nucleus is many

times less susceptible to mutations than its mitochondrial counterpart),


there are many more proteins encoded by genes located in the nucleus: tens

of thousands, versus only thirteen encoded by genes that are in the mito

chondria themselves. So even when a free radical does get into the nuclear

DNA, the odds of it damaging one of the allotopically expressed mitochon

drial genes are many times lower than the odds that it will hit some other

gene. Indeed, many such free radicals will not hit a gene (an instruction for

building a protein) at all, but one of the many stretches of nonfunctional

"junk" DNA. Therefore, the chances of both the mitochondrial copy and the

nuclear backup of the same gene being mutated are vanishingly small.

Moreover, while the unusual design of the mitochondrial DNA ensures

that large deletions in its structure wipe out its ability to synthesize any of

its proteins, the same will not occur in the nuclear case: only the protein for

the specific mutated gene will be affected. Of course, your mitochondria

can't function without all thirteen proteins, but we could help reduce the

risk of any actual shutdown of oxidative phosphorylation—and the result

ing clonal expansion of a mutant mitochondrion—by providing a double

or even triple set of functioning backup copies. 8

The "Mitochondriopathies"

One category of hurdle facing the clinical development of anti-aging bio-

medicines is structural: aging is not a recognized disease, so the FDA will

not allow trials to be performed on interventions claimed to cure it. This is

obviously a bucket of water thrown directly onto the heads of venture cap

italists who might otherwise be interested in investing in startups working

on a treatment for age-related mitochondrial DNA mutations. From the

perspective of getting effective anti-aging interventions into the clinic as

quickly as possible, allotopic expression has the advantage that it is already

being pursued as a treatment for a recognized group of diseases: the mito

chondriopathies.

These diseases are caused by defects in the mitochondrial DNA that

are inherited (or, more rarely, acquired through causes independent of the

aging process). These mutations lead to a failure of energy production that

causes a spectrum of dysfunctions in various organs, depending on the

exact disorder: the brain, heart, and muscles tend to be the most vulnera

ble, but damage can also extend to the liver, kidneys, lungs, and certain

glands. Because allotopic expression is a promising therapy for mitochon

driopathies, government funding (albeit not nearly enough) is already


available for work on its development; and once it is ready to move into

the clinic, there will be an incentive for venture capital to invest in its de

velopment, giving a clear route forward for near-term testing in FDA-

approved clinical trials.

In turn, once allotopic expression has been proven to be safe and ef

fective as a treatment for inherited mutations of the mitochondrial DNA,

we will be in an excellent position to make the small tweaks needed to

adapt it for use as a treatment for mutations acquired during the aging pro

cess. This parallel applicability is a feature of most of the anti-aging inter

ventions included in the SENS platform—and indeed, prototypical

versions of several of the proposed interventions are already in clinical tri

als today.

To Boldly Go Where Evolution Has Gone Before

The other hurdles facing allotopic expression are the more purely scientific

ones. Fortunately, as we will see, progress on these problems has been rapid

in the last decade. But it's better than that: evolution has been working on

a similar job for untold millennia.

In ages long past, the ancestors of the mitochondria occupying our own

cells were not just components of cells as they are today, but organisms in

their own right, which formed an I'll-scratch-your-back-you-scratch-mine

relationship with our one-celled ancestors. Because they were independent

organisms, these proto-mitochondria naturally had a full complement of

their own DNA—at least one thousand genes.

But precisely because the hazardous environment of the mitochondrion

put the genes housed there at extremely high risk of mutation, evolution has

been performing allotopic expression on mitochondrial genes since long be

fore humans appeared on the scene. Over the glacially slow timescales of

evolution, organisms have copied mitochondrial genes that code for mito

chondrial proteins into their cell nuclei, after which the original mitochon

drial genes became redundant components and mutated into oblivion.

And to give Mother Nature her due, evolution has gone a long way in

this direction. Out of more than one thousand original mitochondrial pro

teins, all but thirteen have had their genetic instructions moved into the

nucleus.

Starting in the mid-1980s, scientists started showing that they, too,

could perform allotopic expression of some mitochondrially coded pro-


teins using biotechnology, albeit initially only in yeast—a crucial series of

proofs-of-concept.

Obstacles, Evolutionary and Otherwise

But things get a lot trickier when we start trying to do the same thing with

the thirteen protein-encoding genes that are still located within the mito

chondria in human cells. The reason why evolution hasn't finished the job

for us already is a matter of some debate, but everyone agrees that there

must be some kind of "forces" holding the process back. Whatever those

forces are, this job is probably not going to be easy. What we have to do is

figure out what forces are keeping those genes in the mitochondrion, and

then devise ways of overcoming them. I have a d v a n c e d the case that there

are only two such forces that need concern us. 9

One, which doesn't apply to all organisms but does apply to us, is that

the DNA "languages" of mitochondria and of the cell nucleus have evolved

slightly different "dialects," so that an exact copy of a given mitochondrial

DNA sequence becomes indecipherable when it is dropped into the nu

cleus. This problem is called code disparity.

The case is rather like the changes that have occurred over time in the

writing of the letter "s" in English. Up until the nineteenth century it was

common for an "s" occurring in the middle of a word to be written in an

elongated fashion that looks much more like a modern "f" than an "s ."

Gradually, as writing became more widespread and irregularities in the

written language more standardized, the elongated " s" came to be r e p l a c e d

by the shorter, more curved version of the letter that we use today. Thus a

modern reader of an Enlightenment-era order to launch a naval attack

("Sail for the enemy") might mistake it for a command to "throw" the bat

tle ("Fail for the enemy"), and in other cases an instruction might be re

d u c e d to pure gibberish.

This disparity in the genetic codes of mitochondria and nucleus makes

moving mitochondrial genes that contain such discrepant lettering into the

nucleus a near impossibility for evolution. Indeed, all the genes still housed

in the mitochondria contain such quirks, and this fact alone can explain

why they haven't made the jump to the nucleus. But code disparity doesn't

pose any serious problem for biotechnology: with our outsider's under

standing of the discrepancies in the two codes, we can simply create the

new, allotopic gene using the nuclear version of the code (substitute " s" for


"f") and rest assured that it will be translated and turned into a protein just

like any of the other genes for mitochondrial proteins that are already

housed there. 1 0

The second problem appears to have been a somewhat less imposing

barrier to the evolutionary transmigration of mitochondrial genes to the nu

cleus, but is a much greater challenge for the anti-aging biotech engineer. It

is the repulsion by water ("hydrophobicity") of many of the mitochondrial

proteins whose genes are still located within the mitochondria themselves.

These proteins have sites in their chemical structures that have such a

"fear" (phobia) of water (hydro) that, like a phobic human, they will liter

ally curl themselves up into a ball in response to it.

Hydrophobicity is no problem for proteins when they are built from

DNA that is already located within the mitochondrion, because the final

three-dimensional shape of the protein is supposed to be twisted up, and

there are special enzymes that guide such proteins into the proper confor

mation. But it becomes a showstopper when the same protein is con

structed from DNA located in the nucleus. The genes for such proteins are

translated into their products in the main body of the cell, and the proteins

must then be moved from the fluid environment outside of the mitochon

drion, through the outer and inner mitochondrial membranes, and into

their final location in the mitochondrion's core.

Of course, the membranes won't just let proteins pass freely through

them, or the integrity of the mitochondrion—and its ability to preserve its

proton reservoir—would be compromised by the constant leak of material

into and out of its chambers. But mitochondria do need to be able to import

hundreds of proteins: for example, the dozens of the subunits of the elec

tron transport chain whose genes have already been moved successfully into

the bomb shelter of the nucleus by evolution. Mitochondria have therefore

evolved elaborate machinery that specifically moves (translocates) proteins

through these membranes. These are sensibly called the "Translocase of the

Inner Mitochondrial" membrane (TIM) and the "Translocase of the Outer

Mitochondrial" membrane (TOM), giving the whole system the glorious

name TIM/TOM complex.

The problem is that once a protein has been gnarled into a balled-up

Twister configuration by its repulsion to the water in the fluid compartment

of the cell, the cell becomes unable to jam it through the pores of the

TIM/TOM machinery—rather like trying to force a wildly bent-out-of-

shape coat hanger down a drainpipe. This would be not just a failure, but

actually counterproductive: not only would it prevent the newly allotopically


expressed proteins from getting where they have to go, it would also "clog

up" the TIM/TOM complex, disrupting the import of the many proteins

that were previously being naturally, successfully imported.

In fact, all of the thirteen proteins that are still coded directly in our

mitochondria are very hydrophobic. The instructions for several of those

proteins have never been moved into the nucleus in any species, and those

proteins are the most hydrophobic of all. This suggests that hydrophobicity

is indeed the biggest hurdle to the allotopic expression project. There are

several cases that seem to violate this rule in other species, but I have pub

lished detailed analyses 9 that explain why all of these apparent counterex

amples are misleading—why they would have happened in the course of

evolution despite the fact that hydrophobicity really is the most important

barrier to making the move.

So, if we are to obviate mitochondrial mutations via allotopic expres

sion (my preferred solution), then in addition to the relatively simple task

of editing the code in cases where the DNA "language" of mitochondria

and nucleus are mismatched, we will have to find ways of tweaking the pro

teins that, in their present form, can't be imported into the mitochondria.

When I first began contemplating this problem, I came up with a

workable-sounding but technically challenging way of dealing with it,

which I published in the journal Trends in Biotechnology in 2000. 1 1 I'll de

scribe this approach later on. The reason I'm putting off discussion of this

solution is that recent experiments suggest that we may not need to go to

the lengths that I then proposed in order to overcome the hydrophobicity

problem. There are at least two alternative ways to engineer these proteins

to make them importable—ways that appear to be much easier.

Pirating Mother Nature's Intellectual Property

The first solution to the hydrophobicity problem is to look around for cases

in which evolution has already done the yeoman's work for us—in other

species. We humans (and our evolutionary ancestors) have not yet enjoyed

the simultaneous good fortune of the right random mutations, the right en

vironment and the right selective pressures to pass nuclear versions of any

of these genes along to us as their descendents. But that doesn't mean that

the same happy confluence of circumstances has never occurred in other

species' evolutionary history. Natural selection has been working on the hy

drophobicity problem in many species independently of our own, and has


in several cases come up with workable solutions—solutions that we did

not inherit, simply because they occurred in a separate evolutionary line

age. By looking beyond our own mitochondrial DNA into the evolutionary

inheritance of other species, we might find viable solutions that we only

need to tweak slightly for use in our own cells.

Other species' mitochondrially encoded proteins are not identical to

our own, of course, but their structure is close enough to make it reason

able to believe that they could stand in for the originals if inserted into our

mitochondria, or at least show us how to modify the sequences of the hu

man counterparts to render them importable. If species could be found

whose genes for their versions of some of the thirteen proteins had sponta

neously moved into the nucleus, we would expect to be able to put those

same genes into our own cells' nuclei with only minimal modification.

Those proteins would be constructed in our cell bodies, imported into our

mitochondria, and take the place of the native version if and when muta

tions shut down the mitochondria's ability to do the job themselves.

This idea is not just a fancy of mine: it's been done in isolated human

cells already. Work on such a project began in 1998, shortly after I started

shouting about the importance of a discovery that had been made eight years

earlier, when the mitochondrial genetic library of the green alga Chlamy-

domonas reinhardtii was sequenced. When the proteins for which these crea

tures' mitochondrial genes code were identified by comparison with the

equivalent genes in other species, it was found that they are missing versions

of six of our thirteen hydrophobic electron transport protein genes.

In fact, of course, these genes are rather like your mysteriously "miss

ing" car keys: you haven't actually lost them, they just aren't where you

thought you'd left them. In these organisms, the changes needed to make

these proteins less hydrophobic have taken place, because the greatest bar

rier to the change—code disparity—was never erected. These algae are so

close to the "root" of the evolutionary "tree" that the disparity between the

DNA coding systems of the nucleus and the mitochondrion never took

place in them. Without that hurdle to leap, evolution has only had to ad

dress the much less challenging hydrophobicity problem—and it has done

so with some success. The genetic instructions for these proteins are now

housed in the algal cells' nuclei. The cell's machinery reads those instruc

tions, manufactures the proteins in the main body of the cell, and then the

mitochondria import them—the same thing that happens with most of our

own mitochondrial proteins.

At this point Dr. Mike King at Thomas Jefferson University, Philadel-


phia, comes into the picture. King was not originally interested in aging, but

in the inherited mitochondrial diseases (mitochondriopathies). Researchers

had long dreamed of gene therapy for these disorders, but there are im

mense technical challenges to putting genes directly into the mitochondria.

King thought that allotopic expression in the nucleus could provide a faster

route to a cure.

But the hydrophobicity problem loomed over this potential solution to

inherited mutations in the genes for the thirteen mitochondrially coded

proteins, just as it does for the plan for mitochondrial genes mutated dur

ing the aging process via free radical damage. When he heard about the ex

istence of nuclear-coded versions of some of these proteins in the algae in

the late 1990s, Mike saw that they offered a potential blueprint for replicat

ing the algae's tricks in human patients with mitochondrial diseases.

What followed was an astonishing surge of progress. In 1998, King be

gan a fruitful collaboration with Dr. Diego Gonzalez-Halphen of the De

partment of Molecular Genetics at the Autonomous National University of

Mexico, to identify and clone the algae's genes for the six analogous pro

teins. Within three years, these scientists had identified three of them. One

of these (ATP6, a component of the mitochondrion's Complex V "tur

bine") was of particular interest because inherited mutations in it cause two

rare but extremely serious disorders of the brain and muscular system in

humans: NARP (Neuropathy, Ataxia, and Retinitis Pigmentosa) and mater

nally inherited subacute necrotising encephalomyopathy. In these diseases,

ATP synthesis is r e d u c e d by 50 to70 percent, leading to severe dysfunction

of the neuromuscular system. Thus, the identification of an importable ver

sion of the mutated protein held forth therapeutic potential for people suf

fering from these diseases, as well as for all of us as we age.

Picking up the ball, Eric Schon and his coworkers from the Depart

ment of Neurology at Columbia took the next step, inserting a cloned copy

of the algae's ATP6 gene into the nucleus of human cells whose mitochon

drial DNA harbored the same mutations that cause these neuromuscular

diseases in humans. The cells decoded the genetic instructions, turned out

the protein in the main chamber of the cell, imported it into the mitochon

dria, trimmed off its targeting sequence (a special string of amino acids that,

when appended to the "nose" of a protein, directs it into the mitochon

dria), inserted it into the electron transport chain, and apparently took the

place of the mutated protein, rescuing the cells from the destructive effects

of the mutation. 1 2

In other words, these researchers did exactly what I had been calling


for someone to do. They found, in an alien species, a nuclear gene for a mi

tochondrial protein whose human counterpart is located in the mitochon

drion itself; they inserted it into the nuclear DNA of human cells; and they

showed that those cells could use it in just the way that the algae do, restor

ing near-normal functionality to cells with otherwise disabling mutations.

There is still a lot of work ahead, of course. To turn this into a viable

therapy for people with inherited or age-related mitochondrial mutations,

we will have to do two things. One is to identify in other organisms, or en

gineer ourselves, genes that can be put in the nucleus for the rest of the mi

tochondrially encoded proteins, and show that they restore function to

mutant cells. And the other will be to do the trick in whole organisms bur

dened with these mutations: first in mice (a relatively simple task: genetic

manipulation of mice is now relatively routine), and then in grown humans

(a technology that we have not yet mastered, but upon which work is pro

ceeding with an intensity that may well yield safe, viable therapies in the

foreseeable future).

Borrowed Ideas, Novel Solutions

But of course, there is no guarantee that we will find all of the necessary

genes in other species. It would be smashing luck if we did, of course, but

it's entirely possible that many of the genes for electron transport chain

proteins have never been transferred from the mitochondria to the nucleus

in any species, or that the protein will have been so changed in the intricate

branching of life's evolutionary family tree that it will not work in human

cells. In that case, we'll just have to figure out for ourselves how to tweak

our existing genes to make the proteins they encode importable.

Even here, however, we'll be able to borrow tricks that we've learned

from other species. A remarkable example was reported in 2002, 1 3 when a

group at the University of Western Australia discovered that several legume

species—including the soybean and the common mung bean (Vigna

radiata)—are actually in an intermediate evolutionary state, having evolved

a nuclear copy of the mitochondrial gene for subunit two of the electron

transport chain component cytochrome c oxidase, but without having yet

discarded their original, mitochondrial copy.

The fact that these organisms survive while expressing the protein from

both sites at once is itself good news, as it relieves (to some extent, anyway) a

concern that some people have expressed about using allotopic expression as


a solution to mutations. The worry is that in cells with healthy mitochondrial

DNA and allotopic versions of the electron transport chain proteins, the ex

istence of two independent, working copies of the same gene might lead to

too many copies of the duplicate-coded proteins being produced, and that

this might somehow imbalance or overload the capacity of the mitochondria

to fit the various components together into working electron transport com

plexes. This would be like having two departments in the management of a

factory, each using an independent system to order components for their

product—a serious glitch in any "just-in-time" inventory system. The obser

vation that no such problem occurs in these organisms suggests that we may

not have much to worry about here—and that's good news.

But when other scientists compared the two versions of the legume elec

tron transport gene, they discovered something that makes me even more

bullish about our ability to move the full complement of mitochondrial elec

tron transport chain genes into the nucleus. The two versions of the protein

differ in twenty-five amino acids (the building blocks of protein) out of

hundreds—but only two of these differences are necessary to allow the nu

clear version to be imported into the mitochondria! This suggests that we

may only need to do some relatively minor fiddling with our thirteen proteins

of interest in order to make feasible their import into the mitochondria.

Again, I'm no longer just extrapolating from what evolution has

achieved in other organisms: progress in adapting these solutions to new

problems is definitely under way. Around the same time Schon's group ex

pressed ATP6 in human cells allotopically using the algal version of the

gene, they and another group also reported having developed different solu

tions to the challenge of engineering new, nuclear-coded versions of that

protein. The difference was that these new proteins were not taken

wholesale from another species, but modified from the mammalian original.

As with the success using the algal gene, these human-generated versions

were reported to rescue cells bearing inactive versions of ATP6 in their mi

tochondria. 1 4 , 1 5

Not long after this, a third group engineered a nuclear-coded version of

another mitochondrial gene named ND4, mutations in which cause one of

the mitochondriopathies, Leber's Hereditary Optic Neuropathy (LHON). 1 6

To do this, they first had to find solutions to the problems that had previ

ously been dealt with in the allotopic expression of ATP6. First, the DNA

code for the protein had to be altered to make the "spelling" compatible

with the nucleus, since ND4 suffers from the "code disparity" problem I

discussed earlier. Then, the researchers had to tag on a "targeting sequence"


copied from a completely different gene (aldehyde dehydrogenase) to guide

it into the mitochondria. Next, they had to figure out a way to get the gene

into the nucleus in the first place; this was accomplished using a trick bor

rowed from viruses that sneak their DNA into their infectees' nuclei. And fi

nally, they attached an additional sequence to the gene to allow it to be

picked up by the gene-decoding machinery of the nucleus, so that it would

be "read" and turned into a protein.

Given the need for so many alterations to the original gene, borrowed

from so many different inspirations, you might reasonably be concerned that

something would fail somewhere along the way. But no. The heavily modified

protein, custom-built out of the original by reasoned analysis of what would

be required to make it importable (rather than being copied in whole cloth

from one of our distant relatives), was successfully incorporated into human

cells bearing mutant ND4, which promptly began churning out functional,

mitochondrially targeted ND4. The allotopically expressed protein then

found its way into the mitochondria, took its place in the electron transport

chain . . . and promptly tripled the cells' ATP output, bringing it back to lev

els similar to those seen in normal, nonmutant cells. Not only that: when the

cells were subjected to conditions under which they were forced to lean heav

ily on OXPHOS for energy, these cells with the new allotopically expressed

mitochondrial electron chain subunits enjoyed three-fold better odds of sur

vival than mutant cells lacking the engineered gene.

The researchers boldly concluded that "Restoration of respiration by

allotopic expression opens the door for gene therapy of Leber Hereditary

Optic Neuropathy." I would add that it also puts a large foot into the same

door for the solution of the reductive hotspot problem. Doubts have re

cently arisen concerning the methods used to demonstrate rescue of the

treated cells in two of the above studies, but at least two others are still con

sidered clear-cut.

Inteins: Splitting the Difference

I am hopeful that these two approaches may be sufficient to allow us to

deal with the hydrophobicity issue; however, it is possible that we may have

to go further with some of the very hydrophobic proteins. One potential

solution—which I originally put forward before the above successes sug

gested that it might not be necessary—is to further modify the proteins in

question using inteins.


Inteins are sequences that are inserted temporarily into some proteins

when they are first synthesized, possibly to help the protein mature into its fi

nal form properly, and are then snipped out once they've served their pur

pose. In some cases, the two halves of a final, functional protein are

expressed separately, each with a complementary "semi-intein" at the end

where the two protein segments must finally be joined. When the two halves

of the final protein come together, the two semi-inteins are first bound to

gether, a little like the male-to-female electrical connectors on strings of

Christmas-tree lights. But then the united intein sequence is snipped out and

the two precursors of the final protein are permanently, directly fused to

gether into the final, completed structure.

We might be able to use inteins of this sort to help us deal with a hy

drophobic protein. One approach is to split the protein up close to a site in

its structure where it would otherwise curl up when exposed to water, and

put semi-intein "caps" on either side of the break. As an analogy, imagine

that you wanted to move a long piece of steel with a right angle in its center

(the protein) down a straight drainpipe (the TIM/TOM complex). As it

stands, the job is impossible. But if you could cut the piece of steel at or

near the place where it bends, and then attach a short segment to each of

the severed ends of the bar to show your coworker at the other end of the

pipe where to weld the two halves together again, you could easily drop the

two halves down the tube individually for reassembly at the other end.

Alternatively, whole inteins can actually be built right into the middle

of the two halves of the protein, creating one long structure with the intein

in its center. I'm afraid the way that this can be exploited is a bit harder to

analogize, but I'll try. Imagine if, instead of cutting your bent bar in half

where the bend occurs and sending each half down the drainpipe sepa

rately, you were to cut the bar, rotate it through a half-twist, and put in a

central joining segment, so that the final structure looks more like a stylized

lightning bolt than a right angle. You could then drop the "straightened"

bar (protein complete with intein) down the drainpipe (TIM/TOM com

plex) and then excise the joining segment (intein), allowing you to reassem

ble the bar into its proper configuration after intein removal.

This procedure is a good deal more complicated than switching a cou

ple of amino acids, so I'd rather not have to resort to it if one of the former

options will work. When I first came up with the idea of using inteins as a

solution to the hydrophobicity problem, I foresaw a whole series of poten

tially crippling technical hurdles that might have to be overcome to get it to

work, and I'm still not sure how easy that would be. Inteins would have to


be p l a c e d in just the right place, and be of an appropriate length, and this

would require a lot of fiddling. Also, natural inteins are designed to be

snipped out as soon as the protein that contains them has been con

structed, so mitochondrial inteins would need to be designed in ways that

prevent them from being removed until the complete protein has been im

ported into the mitochondria.

Another problem we might face is that of ensuring that, in the "semi-

intein" version of this approach, the protein segments are joined to their

proper partners. If we have used inteins to break up several proteins that

are imported simultaneously, or if one protein has been broken down into

more than two pieces (as seems likely to be necessary in at least a couple of

cases), the "exposed" ends of protein segments might be mismatched once

the inteins are removed. Fortunately, it appears that some such multiple in

teins do exist naturally and somehow "know" their proper partners, so this

may not really be a problem—and if it is, the alternative solution of putting

inteins into the hydrophobic stretches of these proteins is still available.

Yet another potential headache: segments of proteins could begin to fold

too early, either before joining to their "other halves" in a way that obstructs

access to the fusion site (so that the intended fusion with the mate is no

longer possible), or even right in the midst of the TIM/TOM machinery,

causing the exact problem that the use of inteins is supposed to prevent. And

finally, a protein's separate, newly inteinless segments might be altered by en

zymes while they wait to be joined to their "mates"; any such alterations

could render them nonfunctional, or prevent them from "hooking up."

The good news is that, despite all of these potential obstacles, at least

one split intein job has already been pulled off in cell culture: 1 7 Yoshio

Umezawa and coworkers took an unimportable green fluorescent protein

and in t roduced it into a cell's mitochondria by first adding on a borrowed

mitochondrial targeting sequence, and then adding inteins inserted into its

structure using a protein splicing system taken from algae, before finally

"infecting" the cell's DNA with the composite structure's code. The result

was that the protein was indeed expressed and imported into the cell's mi

tochondria, where it allowed the scientists to detect the presence of other

proteins that they were trying to direct into the organelle.

G E T T I N G O F F T H E G R I D 97

Not TINA but TATA

This string of successes indicates that we can expect rapid progress in ex

pressing the remaining mitochondrially coded proteins from nuclear genes

in reasonably short order, through some combination of the different tech

niques I've discussed here. Once we have figured out how to put all thirteen

of these proteins' genes into the nuclear "bomb shelter," we will be very

close to being able to negate the insidious effects of mitochondrial mutations

in aging, turning existing "reductive hotspots" into normal, healthy cells

and preventing the formation of new ones. When that is accomplished, we

will be able not only to stop but to reverse the slow upward creep in oxida

tive stress—and the accelerating spiral of molecular damage and metabolic

disruption—that we think is driven by these mutations today.

But, of course, the precedent of medical history tells us that some pit

falls may still lie in wait for this solution. One can make one's most edu

cated predictions, based on a sober consideration of the published science,

and still fail to anticipate an intractable roadblock. My biggest worry is

that, even after a bit of tweaking, the volume of TIM/TOM traffic required

to import the new allotopically expressed proteins will be so high, and its

rate of flow through the system so slow, that we will not be able to transfer

the full complement of proteins via this route even if we succeed with each

of them individually. I am especially concerned about this since some of the

proteins that have been allotopically expressed move quite poorly through

the TIM/TOM machinery; one of the examples we discussed above in

volves a protein that is only incorporated into the mitochondria at 40 per

cent of the efficiency of the native, mitochondrially-coded version.

Former prime minister Margaret Thatcher, the "Iron Lady," was fa

mous for intoning "There Is No Alternative" (TINA) to the neoliberal eco

nomic agenda. I have no intention of painting myself into an ideological

corner over my preference for allotopic expression: lives are at stake, not

just my ability to admit that I'm wrong. I will instead join the ranks of her

anti-globalization critics, who spilled into Trafalgar Square in their thou

sands chanting "Not TINA but TATA!"—that is, "There Are Thousands of

Alternatives."

Having made that bold declaration, I hasten to add that I think we can

safely trim down "thousands" to "a few, and even fewer that are viable." In

fact, quite a number of alternative fixes for mitochondriopathies have been

advanced, and at first glance these solutions might also be expected to treat

age-related mitochondrial DNA deletion accumulation. Unfortunately, I


predict that most of those solutions will be of no help in preventing the de

velopment of "reductive hotspots," because the mechanism whereby the

underlying mutations accumulate (mitochondrial free radical generation

and clonal expansion through the Survival of the Slowest) is quite distinct

from the mostly inherited problems in mitochondriopathy victims. Re

search toward cures for mitochondriopathies using these alternatives will

still doubtless yield techniques and insights that will in some way help us to

develop a cure (via allotopic expression or some other therapy), but I do

not believe that most of these will be adaptable as anti-aging biotechnology.

I shot down the major flawed proposals down in the 2000 article in Trends

in Biotechnology that I mentioned earlier. Two approaches exist that I feel

have much more promise, however.

One, a d v a n c e d by Drs. Rafal Smigrodzki and Shaharyar M. Khan of

the Center for the Study of Neurodegenerative Diseases at the University of

Virginia, starts with the ability to introduce into the mitochondria modified

versions, not of individual genes (as in the classical gene therapy approach),

but of complete copies of the entire mitochondrial DNA. They accom

plished this maneuver—which they have termed protofection18—using

boldly simple techniques that most scientists would have dismissed as un

workable. It's too early to say how versatile and repliable their method is,

though—it's too new to have been explored by other scientists.

The other very promising alternative to allotopic expression is to intro

duce genes for alternative versions of the mitochondrially encoded en

zymes, versions that don't quite work the way that the native ones do. The

enzymes in question already exist in—and could thus, in theory, be bor

rowed from—some lower organisms (yeasts and plants). They perform the

exact same electron transport activities of the enzymes that we partly en

code in our mitochondrial DNA, even though they themselves are not par

ticularly hydrophobic and are encoded in their species' nuclear DNA. The

problem—if it is one—is that they only do the electron transport, not the

proton pumping. But introducing them into our cells might be a fair trade

off, because while they would not restore the mitochondrially mutant cell

to its full capacity, they would prevent these cells from impairing the ability

of the rest of the body to get on with the business of life. This has actually

been documented in isolated human cells: when Complex I is chemically

inhibited, normal cells quickly die off, but cells given the relevant yeast

gene remain viable. 1 9

One problem with this proposal is that, if these proteins were to be ex

pressed in cells that had not suffered deletions, they would deny the cell of


much of its energy source. We would use one gene to bypass the first enzyme

in the electron transport chain (Complex I) and another to bypass the rest.

Neither of them pumps protons, so having both of them substituting for

much of the native, proton-pumping complexes in a mitochondrion would

seriously impair the buildup of a proton "reservoir" and, thus, ATP produc

tion. This could lead to anything from a mild functional impairment to a se

vere energy deficit—and it would extend through every cell in the body, not

just the "evil 1 percent" of cells with a population of mutant mitochondria.

This would leave us in a very bad way indeed, so we would need to find a

way to ensure that the genes for these "bypass enzymes" are expressed only

in cells whose mitochondria are no longer producing the native proteins.

There is no obvious way to do this at the moment, unfortunately. But luckily,

initial research indicates that these enzymes naturally possess a system that

activates them only when their proton-pumping counterparts are failing.

Even expressing one of the two "bypass enzymes" indiscriminately would

make cells less efficient at making ATP, so this is actually no surprise.

The Way Forward

Overall, the picture is a rosy one. We have not only a good idea of how mu

tations in the mitochondrial DNA contribute to the age-related decay of our

bodies, but a clear path forward to obviating the problem—even if our un

derstanding of the exact mechanistic link between mutations and pathology

turns out to be mistaken. Allotopic expression would allow our mitochon

dria to keep functioning normally even when their DNA acquired muta

tions; protofection, alternatively, could simply clear out the old mutant

DNA periodically, replacing it with a fully functional new set of genetic

blueprints; and the use of easier-to-handle enzymes that pump no protons

but keep electron metabolism harmless would at least keep mutant cells

from causing trouble outside of their own membranes.

Again, we will need to develop safe, effective, stable gene therapy that

works in grown humans in order to turn any of these interventions into a

real biomedical intervention against this aspect of the aging process, and

that will certainly be a challenge. But, again again, it's a challenge that sci

entists all over the world are already vigorously pursuing in order to treat

genetic disorders—ailments ranging from Huntington's disease, to inher

ited cancer risk, to familial Alzheimer's disease, to sickle-cell anemia. And

we can piggyback even more closely on research that is specific to the


mitochondriopathies—a much smaller field, but one that, for the moment,

still receives more serious funding and attention than work designed to

tackle the slow-motion global plague that is aging.

With the resources already being thrown at advancing gene therapy, we

can confidently predict that the clinical readiness of this enabling biotech

nology is foreseeable. I am therefore convinced that the major hurdle facing

speedy implementation of allotopic expression (or its alternatives) will not

be our ability to develop safe gene therapy for patients, but the dearth of

investment into the basic science of moving mitochondrial genes into the

nucleus.

Remember the positive result using inteins to import proteins into

mitochondria in culture? This achievement came about because scientists

were seeking a way to get rapid feedback on the results of a completely un

related project of interest to them. Imagine what could be accomplished

with resources specifically dedicated to developing allotopic expression for

the purposes of reversing aging damage!

How to bring about that change in research priorities is the subject of

Chapter 15; but now, let me take you on a tour of the next of the "Seven

Deadlies" of aging, and show you what we can do about it.

7

U p g r a d i n g t h e B i o l o g i c a l

I n c i n e r a t o r s

Just like our own households, cells generate garbage as an

inevitable result of their normal functioning. Again like

households, they are able to dispose of most of this waste—

though they recycle a proportion of it that would put

the most eco-friendly household to shame. But cells cannot recycle

quite all the junk they create, and the portion that escapes

destruction accumulates, to the cell's eventual detriment. Several

years ago I devised a new approach to this problem that

exemplifies, perhaps better than any of my other contributions to

this field, the value of the widely cross-disciplinary expertise

that is so rare in biology today.

Mary Shelley c o u l d n ' t ask for a more perfect scene, I thought, as I

sank my trowel into the scruffy graveyard sod.

A quick scan of the horizon at Coldham's Common would initially

make you think it was a nondescript, even rather dull little field in the heart

of England. But knowing its history transforms your view of the spot, open

ing the mind's eye to a bleak, windswept stretch of near wilderness,

dropped as if out of a Gothic horror novella into the midst of a plain

bounded by football grounds and parking lots, bisected by a railway line.

Though it is sometimes used for public events or cattle grazing, it spends


much of the year lonely and abandoned, its sole claim to fame arising from

its association with mass death.

In the late seventeenth century, the Great Plague swept its scythe

across England. When its icy fingers crept into Cambridge, the plague

claimed a third to a half of the residents—including sixteen of the forty

professors at the University—and sent the young Isaac Newton fleeing for

his life. In its wake, the survivors hastily plowed most of the plague's vic

tims anonymously under the unhallowed ground. Even before it became a

mass grave, the area bore the taint of association with infection and death:

its most enduring landmark is the remains of Cambridge's twelfth-century

Leper Hospital. As if to complete the cliche, on most days of the year Cold-

ham's Common is documentably several degrees colder than the cobbled

streets that surround it.

The scene, then, was complete: I, the "mad scientist" (complete with long

beard and pale, sunless skin), surrounded by Cambridge's Enlightenment-era

faux-Gothic castles and cathedrals, had hopped my way with an irrational

furtiveness over multiple fences into the last resting place of the mortal re

mains of untold scores of lives, and was now digging into the soil of a mass

grave, in hot pursuit of the secrets of Life and Death.

Victor Frankenstein, eat your heart out.

I must confess that the above account incorporates a small amount of

poetic license: the person who performed the above task was not I but a

graduate student in my University of Cambridge department, and actu

ally she retrieved the soil sample from Midsummer Common, not the

nearby Coldham's Common. But that's by-the-by. To understand what

she was doing there, let's take a detour out of the graveyard and into the

junkyard.

The Waste of Your Life

Whether we toss things into the garbage bin without a thought, or

painstakingly wash and sort our recyclables, we in the developed world

generate an astounding amount of waste material every day. When we de

cide that we don't need something anymore, or that it's too damaged or rot

ten to be worth our efforts to salvage, we simply stuff it into a bag or bin

and put it out for pickup, confident that the unsung heroes of the sanitation

department will take it away and out of our concern. Thanks to an efficient

waste-disposal infrastructure, a truly remarkable volume of waste material

U P G R A D I N G T H E B I O L O G I C A L I N C I N E R A T O R S 103

can pass through our homes, workplaces, and streets—yet these places

remain clean, pleasant-smelling, and sanitary.

It wasn't always this way, of course. For most of the history of civiliza

tion, the streets of our cities were literal cesspools, into which the citizens

hurled their trash and human waste directly out of their windows without

care for what—or even who!—was below them. Most of us truly cannot

imagine what foul, malodorous, and dangerous places cities were until quite

recently. The toll of living in such a toxic environment can be seen in the

disparity of life expectancy for people living in different environments in

seventeenth-century England. An Englishman would typically live to be

thirty to forty years old if he lived in the countryside, but if he lived in

London, he could expect just twenty-one to thirty-four years of life.

Anyone who's lived through the kind of big-city garbage strike that

nearly paralyzed London in 1976 has an idea of just how vital a functioning

waste-collection system is for health and the carrying-on of the business of

daily life. In shockingly short order, trash can literally be piled ten feet into

the air, in precarious piles that fall apart in the wind or as new bags are

added to the crude structures. And the mountains of garbage are not

merely unsightly: Aside from the smell, the garbage attracts vermin, and

with it, disease—particularly when the contents of the trash bags begin to

spill onto the street because of attacks on the bags by animals, the elements,

or the putrefaction and liquefaction of its contents. Sidewalks become in

creasingly impassable, and even street traffic may be impeded. People be

come less willing to leave the house or go into shops. A strike that lasted

just nine days in 1968 came close to bringing New York City to its knees.

Well, something similar happens to your cells as they age—except that

in a sense it's worse. Rather than a temporary "interruption of service," ag

ing cells undergo a progressive degeneration of their waste management in

frastructure that would make the worst examples of inner-city decay look

like models of sanitation.

Two chapters ago, in discussing the process whereby mutant mitochon

dria "clonally expand" to replace all of their genetically healthy cousins in

the cell, I in t roduced you to the lysosome—an organelle that I called the

cellular "incinerator." Actually, "recycling center" would be a more precise

metaphor than incinerator, because a lysosome's job is not to out-and-out

destroy cellular wastes, but to break them down at the molecular level into

more basic components that can be used as raw materials for the biosyn

thesis of new cellular membranes, enzymes, and other important compo

nents of the cellular machinery. The incinerator metaphor is meant to


convey the extraordinary power of the lysosome's molecular-level dismem

berment of the materials that are thrown into it, as well as the chemical na

ture (burning is a chemical reaction, remember) of the lysosome's methods

of breaking down waste into its fundamental components.

While the cell actually has a variety of mechanisms for reprocessing

damaged cellular constituents, its lysosomes deal with some of the nastiest

of them, including the waste materials that are still left over after the other

cell waste-disposal systems have had a go at them but failed. In addition,

when those alternative waste disposal units themselves become worn-out or

damaged, it falls upon the lysosomes to break them (and, often, their semi-

digested contents) down. This chapter is about what goes wrong with the

cell's scrapyards of last resort and how we might avert that process.

» - * P Cleaning Up Life's Messes

Your cells, like your household, are constantly producing and consuming

goods and generating wastes of various kinds in the process. One sort of

waste is akin to packaging, or disposable pens, or tacky old bric-a-brac, the

possession of which has come to embarrass you. It may have served a pur

pose at one time, but today you have no further use for it and wish it gone.

Many cellular constituents are like this: Enzymes and signalling molecules

are "disposable," p r o d u c e d for temporary or even one-time use in response

to the immediate conditions in or around the cell, and they need to be de

graded once they've served their purpose.

Another type of waste is more like something for which you would still

have a use, except that it can no longer fulfill its purpose because it's been

broken. Just as you can turn a piece of your grandmother's china into a jig

saw puzzle, or make your shirt unwearable at work by spilling dark red

wine on it, so components of your cells—from the small (individual en

zymes) to the very large (entire organelles, like a mitochondrion)—can be

come incapable of performing their vital cellular function after suffering

molecular damage at the hands of free radicals and other products of the

dirty underside of metabolism.

And a third type of waste is genuinely toxic material. Just as a useful

substance (say, cottage cheese) can become a threat to your health through

chemical changes (such as being taken over by mold), so normal cellular

constituents sometimes become toxic to the cell through modification of

their structure, or through being present in excess. As surely as, upon en-


countering the new ecosystem growing in your cottage cheese, you seal the

container and drop it from shoulder level into the garbage, so, too, the cell

needs to eliminate similar threats to its functioning.

Recycling's Dirty Details

All of this waste (except, again, that which is destroyed by simpler machin

ery) is directed to the cell's lysosomes. Functioning lysosomes ensure that it

gets properly processed, removing toxic by-products of normal cellular

machinery, returning usable molecular building blocks to the cell from the

"slag" of the broken-down components, and making room for healthy, func

tioning cellular constituents.

So what exactly are these cellular incinerators? Lysosomes are

membrane-bounded organelles packed full of a variety of enzymes, each of

which evolved to target a "weak spot" in the chemical structure of a waste

product that will accumulate in our cells and kill us if it isn't broken down.

A lysosomal enzyme first binds to a waste product that carries the kind of

chemical structure that it evolved to destroy, and then twists its shape like a

tiny biological crowbar, physically tearing apart the target material's molec

ular joints. This is generally accomplished by a type of chemical reaction

called hydrolysis, which is why such enzymes are called hydrolases (hydro

being the Greek for water, as in "hydroelectric").

The exact chemical details of this process aren't terribly important for

our purposes, but you should be sure to remember one key point. In order

to break down a given waste product, the lysosome must have two things:

the right enzyme for the job (one that targets a vulnerability in the structure

of the specific waste product in question), and enough acidity in its interior

for the relevant enzyme to function. This latter is required because differ

ent levels of acidity cause enzymes and other proteins to assume slightly dif

ferent shapes, so that when the acidity in the lysosome is wrong, the enzyme

becomes "bent out of shape" and thus no more able to do its job than is a

flattened-out crowbar. Acidity is also required for the functioning of pro

teins that translocate some waste products into the lysosome in the first

place, so that a mild neutralization of the lysosome's acidity prevents junk

from even being delivered to the recycling center to begin with.

Lysosomal enzymes, like other cellular proteins, are created out of the

blueprints present in the nuclear DNA. They are then shipped into the

lysosome, though by machinery very different from the mitochondrion's


TIM/TOM complex. The extra protons that create the lysosome's acidity

are actively pumped out of the main chamber of the cell and into the lyso

some by an energy- (that is, ATP-) consuming pump located on its mem

brane (the vacuolar ATPase).

Incomplete Combustion

You won't be surprised to learn that bad things happen if your body fails to

produce a lysosomal hydrolase that is needed to break down a waste prod

uct being p r o d u c e d in some cell type—or if it produces a defective form of

the protein that doesn't do its job properly. In fact, this is precisely the de

scription of a group of rare but well-established genetic disorders known as

lysosomal storage diseases (LSDs).

There are about forty such diseases, but luckily only about one person

in 7,500 is born with any of them. Victims of all of these diseases suffer

from one or another type of failure of their lysosomal incinerators. Many of

them completely lack the gene for a lysosomal enzyme, or bear a mutated

copy of it, resulting in a misshapen and ineffective version of the hydrolase.

In other cases, the problem is that one of the specialized transport proteins

on the surface of the lysosomal membrane is missing or defective, so that

the lysosome can't bring the junk into itself to break it down.

No matter what their origin in a given patient, the result of such muta

tions is a deadly degenerative disease. Which organs a given mutation affects,

and how severely, varies from one LSD to another, depending on exactly

which missing or malfunctioning enzyme is at the root of the problem. This is

because different cell types produce different wastes at different rates, and

each particular waste exerts a distinct pathological impact on the cell if it isn't

degraded.

But in all cases, patients suffer pathology in major organs. In Gaucher

disease, the spleen swells up and anemia develops. There are two inherited

forms of Niemann-Pick disease. In the fast-acting version (Type A), the

liver and spleen enlarge and the nerves degenerate starting at birth, killing

its victims by age two or three. In the slower-acting variety (Type B), pa

tients may develop fatty, yellow nodules on their eyelids, neck, or back, and

an enlarged liver, spleen, and lymph nodes. And Hurler syndrome causes

facial features to twist up and bone deformities to occur, along with en

largement of the spleen and liver, joint stiffness, clouding of the eye, early-

onset dementia, and hearing loss.


The exact mechanistic links between the lack of effective waste dis

posal and particular pathologies have not all been worked out in detail, but

the basic picture is clear. The undegraded waste material accumulates in

the lysosome, causing it to swell up and take up too much room in the cell,

impeding the traffic of other materials in the main cell body. Meanwhile,

the acids and enzymes within the lysosomes are diluted, inhibiting their

ability to both import and break down other wastes for which the cell does

have the requisite enzymes, thereby setting up a vicious cycle.

There are also some cases in which it appears that toxic, undegraded

waste accumulates in the main body of the cell. This can be either because

it is not trafficked into the overburdened lysosome in the first place, or else

because the failing organelle starts to leak or even bursts, spewing its toxic

load—including the acids and enzymes that it carries, which are essential to

lysosomal function but potentially deadly to the rest of the cell.

Lysosomal Limitations and the Deadly Dregs

In addition to the terrible, early-acting pathologies that ravage the victims of

these genetic disorders, however, it's also long been known that undegraded

gunk builds up in the lysosomes of all of us as we age. Called lipofuscin (LIP-

oh-few-sin1) or popularly "age pigment," this noxious, accumulating goo is

a chemical hodge-podge of fatty and proteinaceous materials derived from

membranes, reactive metals like iron and copper, and a variety of other or

ganic molecules. It is easy to see with a microscope because it glows red

when exposed to light of a particular wavelength.

Lipofuscin is actually not a single, specific compound, but a catch-all term

for the mixture of stubborn waste products that refuse to be broken down af

ter they've been sent to the lysosome for degradation—materials so chemically

convoluted that the normal complement of lysosomal enzymes just doesn't

know how to deal with them. A combination of damage from free radicals and

from glycation (the random sticking-together of different "branches" of a sub

stance's proteins by reaction with the sugars in your blood and cells) twists

their structure back on itself like some demented child's molecular origami,

burying the vulnerable spots in their structure so that lysosomal hydrolases

can't get at them to break them down.2 As a result, these materials don't get

properly degraded—and because lysosomes are in most cases unable to ex

port them out of the cell, the material just accumulates, taking up more and

more room in the lysosomes of long-lived cells like the heart and the brain.


First spotted in the nineteenth century, lipofuscin was largely ignored

by biomedicine until it became a hot—and controversial—topic in biogeron

tology in the 1970s. At that time, it seemed just obvious to many researchers

that lipofuscin must be bad for us: it slowly fills up our cells, (taking up as

much as 10 percent of the total space in aged primates' heart muscle cells,

for example), and the course of its accumulation tracks the cell dysfunction

seen in aging animals (including people). Indeed, the rate at which lipofus

cin accumulates in a given species' heart was found to be proportional to its

rate of aging, so that adolescent, middle-aged, and old monkeys of two dif

ferent species, with greatly different calendar ages but at similar stages in

their life cycle, have roughly the same level of lipofuscin clogging up their

cells. Many researchers outlined a mechanistic hypothesis of lipofuscin as a

contributor to aging similar to what happens in the LSDs: lysosomal fail

ure, waste accumulation, interference with cell trafficking, and the release

of toxic enzymes and acidity from ruptured lysosomes.

But the point was a contentious one. Many scientists believed that lipo

fuscin was benign, in part precisely because it is so hard to degrade: With

the reactive spots in their structure already balled up and stapled together

by previous free radical and glycation damage, lipofuscin is chemically

quite inert, so it doesn't interact with essential biomolecules the way that

free radicals or other toxic chemicals do. Also, speeding up the accumula

tion of lipofuscin in experimental animals by denying them adequate vita

min E did not shorten their lives, as one would expect of any manipulation

that accelerated a real cause of aging.

But those reports were strongly disputed by other experts in the field,

because it was not at all clear that the material whose accumulation was in

creased by vitamin E deficiency actually was lipofuscin. Much of what gets

referred to by this name in the older scientific literature is actually other, re

lated substances (often called ceroid) that share many of lipofuscin's prop

erties but are much easier for the cell to break down. It seemed likely that

vitamin E deficiency was increasing the production of this relatively

tractable material, while levels of "real" lipofuscin were unaffected.3 More

over, while ceroid accumulation was associated with a variety of diseases

(diseases in which normally degradable substances are not degraded—one

could think of them as nongenetic LSDs), it was not clearly related to "nor

mal" aging.

And so, the debate went 'round. As with many such cases in the early

days of biogerontology, the data were ambiguous, the definitions were im

precise, and there was little hope of a clear resolution.


I had, myself, remained an agnostic on the subject up to and including

the writing of the first draft of my doctoral thesis. But that began to change

in the spring of 1998, when I met Ulf Brunk, chair of pathology at Sweden's

University of Linkoping, at the Oxygen Radicals Gordon Conference in

Ventura, California. After listening to his presentation of his recent results, I

started taking lipofuscin more seriously as a potential nexus connecting the

intricately orchestrated chaos of metabolism to the pathology of aging.

Brunk had done some first-rate work in assessing the role of lipofuscin

in cultured heart cells—an important technical advance, especially because,

in the body, heart cells never divide. When a cell divides, its load of cellular

junk—including lipofuscin—is shared between the two daughter cells. Each

now has half as much, on average, and this will continue with each new gen

eration. If the junk is only being generated quite slowly, this dilution process

will fully balance the rate of creation of new junk and an unmanageable level

of junk will never accumulate. The quickly replicating skin cells that had

been used in much previous work did just this—they tended to dilute Out

lipofuscin and other cellular junk, and so could not replicate the real effects

of lysosomal buildup in critical nondividing cells like those of the heart and

brain. This had long been recognised, but heart cells had been found to be

notoriously hard to culture—in large part, it turns out, because of the high

levels of oxygen in the atmosphere. Cultured cells are still too often grown

under normal atmospheric air, despite the fact that our bodies ambiently

contain only about one seventh of air's concentration of oxygen.

By growing the longer-lived heart cells under more physiological levels

of oxygen, Brunk was able to show how increased oxidative stress—higher

levels of free radical damage, in other words—increased lipofuscin forma

tion. He also confirmed previous suspicions about how lipofuscin accumu

lation could impair the ability of the cell to recycle its used-up components.

And on top of that, he was also able to show that older heart cells accumu

late damaged mitochondria—which they would not do if the lysosome were

operating properly, since the disposal of defective cellular power plants is

one of their chief responsibilities in the cellular economy.

With his collaborator Alex Terman, Brunk outlined a "garbage catas

trophe" theory of aging, 4 in which accumulating lipofuscin inside the lyso

some dilutes the organelle's acidity and supply of enzymes. In this model,

lipofuscin also wastes a lot of the enzymes that the cell body produces, by

sucking them up without making effective use of them, thereby diverting

them away from the other, still-functional lysosomal contents against which

they could be put to effective use.


As the cell's lysosomes accumulate waste products that they aren't

equipped to handle, they become ever less able to break down materials

within them. As a result, the junk in question spends more time either out in

the main body of the cell, or even trapped inside the lysosome, before being

"incinerated." During that time, chemical alterations continue to occur in

the structure of these wastes, mangling them further and further and making

it more and more difficult for lysosomal hydrolases to reach the weak spots

in their structure. As a result, even the standard cellular junk that lysosomes

are, in theory, well equipped to degrade is no longer efficiently broken

down, but instead accumulates—which then further dissipates the hy-

drolytic enzymes and acidity of the lysosome. In their culture experiments,

Brunk and Terman showed that lipofuscin overload could even trigger cell

death, as lysosomes become loaded with the stuff and rupture.

The data underlying this model were compelling, and I liked it at once,

sneaking a short reference to it into my Cambridge biology thesis.5 But I

wasn't yet convinced that lysosomal failure was truly a significant contribu

tor to aging, because if the theory were right you would expect to find evi

dence connecting lipofuscin to actual age-related disease, and no such

evidence initially turned up when I went looking for it.

I quickly learned, however, that this seeming lack of data was more of a

communication breakdown than an information vacuum. Researchers tend

to get holed up in their narrowly specialized fields of study, and conse

quently they, too, rarely compare notes and observe the confluence of ob

servations in different fields of science (or even subfields within those

fields). I soon found that if I stopped specifically talking about "lipofuscin"

and began asking researchers about the importance of lysosomal dysfunc

tion in the diseases that they studied, I was suddenly inundated with evi

dence that the accumulation of junk that should be processed in the

lysosome was at the heart of the matter—but that this fact was being ob

scured by the use of specialist jargon in referring to those wastes.

Making the Link to Pathology

A t h e r o s c l e r o s i s

Just over a year after I was first exposed to Brunk's suggestive data, I was at

tending the biennial Gordon Conference on Atherosclerosis, at which I

found myself listening to a review on the complex processes that lead some-


one from having too much cholesterol in the blood, to having fatty plaques in

the arteries (atherosclerosis), to having diagnosable coronary heart disease

and eventually a heart attack. As I quickly learned, researchers had been

placing lysosomal failure at the core of the molecular events that underlie the

formation of atherosclerotic plaques for years before I began looking into the

issue—and they did so without ever mentioning "lipofuscin."

Most people visualise atherosclerotic arteries as being much like

clogged pipes. Greasy gunk (whether it's bacon fat or blood cholesterol)

simply accumulates on the inside of the tube, coating its surface and clog

ging it up, and blocking the passage of fluids—be those fluids the dishwater

in your sink or the blood in your arteries. In fact, however, we've known for

some time that the process is much more complicated than this. 6 Athero

sclerosis begins with a microscopic problem in the blood vessel wall. Many

things can cause or contribute to this, including friction from the passing

torrent of blood flow, or the force of high blood pressure, or infection; most

often, however, it's just the accumulation of our old friend LDL, low-density

lipoprotein, which has a tendency to get stuck there. The body responds to

this problem just as it does to any other injury: by secreting factors that in

flame the site in order to attract immune cells called macrophages.

Macrophages then infiltrate the damaged tissue to help it heal by cleaning

up the debris.

I didn't tell you very much about LDL in Chapter 5; now's the time for

more detail. Despite its bad reputation, cholesterol is actually a necessary

component of cell membranes. In fact, the so-called "bad" cholesterol

(LDL) in the blood is actually a carrier particle, designed by your body to

bring needed cholesterol to cells, and those cells in turn have specialized

receptors designed to allow them to ingest it for their internal use.

In order to reach most cells, the cells that comprise the walls of our

blood vessels must allow LDL to pass between them, and beyond into the

surrounding tissue. But when cholesterol is chemically modified—by expo

sure to free radicals (oxidized LDL) or reactions with blood sugar (glycated

LDL), for example—it becomes more prone to stick together and thus

more immobile. Because free radicals and blood sugar are (respectively) in

evitable by-products of, and necessary raw materials for, some of the most

fundamental metabolic processes in the body, they are ubiquitous. Hence,

LDL particles are constantly being subjected to their chemically disruptive

influence. Furthermore, enzymes that are designed to call in immune cells

when the vessel wall is injured also alter cholesterol in ways that make it

more toxic.


That's the main reason why having a high cholesterol level is bad for

you. The more cholesterol there is in your blood, the more contact it has

with these damaging agents, and the more toxic, modified cholesterol will

be coursing through your body.

So, when macrophages are attracted toward an inflammatory signal,

they find plenty of junk in need of removal. Initially, macrophages deal rea

sonably well with the gunk that they're internalizing, and they can often

successfully remove the detritus. But when an already compromised blood

vessel continues to be assaulted by high blood cholesterol levels, inflamma

tory signals created by excess body fat, or nasties from cigarette smoke, the

problem persists and macrophages hang around for longer.

As they take in more and more waste—particularly an excess of modi

fied LDL—macrophages begin to fall behind in their work. An increasing

percentage of the load of junk is not successfully processed, but instead ac

cumulates within the macrophages' lysosomes—or, just as bad, is puked

out of the lysosomes without being properly detoxified, forming droplets of

modified cholesterol in the cell body.

As this continues, macrophages eventually become the cellular coun

terparts to the obscenely bloated "Mr. Creosote" in the restaurant sketch

in Monty Python's The Meaning of Life. If you've seen this movie, you

will definitely remember the scene. Mr. Creosote comes into a fine French

restaurant already stuffed with food and badly nauseous, but is plied with

"moules marinieres, pate de foie gras, Beluga caviar, eggs Benedictine" and

sauces "rich with truffles, anchovies, Grand Marnier, bacon and cream" by

the perversely codependent and outrageously "French" maitre d' (John

Cleese).

Creosote becomes more and more ill as the meal progresses, but when

he finally attempts to summon up the will to stop eating he is cajoled into

having just one last "wafer-thin" after-dinner mint. When the spineless pa

tron swallows the mint, a look of helpless horror fills his face; as the maitre

d' runs for cover, Creosote literally explodes, his innards and lunch splatter

ing graphically over staff and guests alike.

Imagine your blood vessels to be such a restaurant, welcoming a steady

stream of customers just like Mr. Creosote in the form of macrophages that

come in to dine on modified cholesterol products. Imagine that they simply

refuse to leave when you're trying to close up, but continue to stuff them

selves until their "stomachs" (lysosomes) can't take any more—and then

keep going until it kills them, and your restaurant (blood vessels) becomes

their final resting place.


You now know, in essence, the genesis of the "foam cells" that accu

mulate in your vessel walls, forming "fatty streaks" as they become numer

ous enough to be seen with a microscope, and eventually developing into

full-blown, unstable atherosclerotic plaques—the scabbed-over messes

that ultimately form at the injury site, crammed with a miasma of clotting

blood, inflammatory signal molecules, and dead foam cells. Once this hap

pens, your days are numbered. It's only a matter of time until the pressures

within and without the plaque cause it to rupture, spewing its contents into

the bloodstream. This content is not a liquid but a horde of semisolid

chunks, and these chunks are rapidly swept from their origin in the major

arteries into progressively smaller vessels. They become stuck there, block

ing off the flow of blood—sometimes into the heart (causing a heart at

tack), sometimes the brain (causing a stroke).

So we now understand that lysosomal dysfunction is the key step in

the conversion of healthy macrophages into undead foam cells—and of

healthy blood vessel tissue into an atherosclerotic time bomb. This fact is

widely recognized, but unfortunately, nearly all researchers are pursuing

old-school, ultimately preventive treatments for the problem. Existing

anti-atherosclerotic drugs try to prevent macrophages from stuffing them

selves so badly, either by reducing blood cholesterol levels or by reducing

LDL's exposure to metabolically active agents (blood sugar, inflammatory

enzymes, and free radicals). Drugs currently in the pipeline seek to ap

proach the same problem from its flip side, by increasing the transport of

cholesterol out of the blood, cells, or organs before it gets a chance to do

its damage.

Meanwhile, basic researchers working in areas other than drug devel

opment are spending a lot of time trying to puzzle out exactly what causes

macrophages' lysosomes to fail, with the idea that, if they understood the

fine details of the process, they could design drugs that would interfere in

the relevant steps in the metabolic chain. Unfortunately, the evidence is

consistent with many interpretations, and the data are difficult to reconcile,

which has more-or-less stalled progress in developing therapies based on

this model.

For instance, some researchers focus on the fact that, in test tubes, oxi

dized cholesterol inhibits the necessary processing ("de-esterification") of

normal (unmodified) cholesterol in the lysosomes, slowing it down enough

to create a deadly backlog. Others think that modified LDL, like lipofus

cin, is itself undegradable, and dilutes out the factors needed for the lyso

some to degrade other materials as it accumulates. There is also evidence


that something in modified LDL (or some metabolic by-product of it) is

harmful to lysosomal function—such as the evidence (again in test tubes) that

the oxidized cholesterol variant 7-ketocholesterol (7-KC) interferes with the

activity of the membrane-bound ATPase enzyme. When this enzyme is im

paired, it can't maintain enough acidity in the cell's lysosomes to keep their

hydrolases working properly, so there are those who think that this is where

we need to look for a solution. And still others think that macrophages sim

ply take in too much LDL, so that its sheer volume overwhelms their pro

cessing capacity; if so, slowing uptake might also slow down the development

of the disease.

As yet, we don't know which school of thought is correct—and it's un

likely that we will resolve the question definitively any time soon, because

the conditions under which the relevant studies are carried out are so un

like what happens in the body. While the scientific debates continue, vas

cular disease caused by atherosclerosis remains the number one killer in

the developed world—and other problems that arise from the same failure

to process cholesterol may be related to a wide range of other age-related

diseases.

Fortunately, an intervention that came to me in a flash some years

ago 7—and that has since been worked out in greater therapeutic detail in

collaboration with others8 , 9—offers a solution that sweeps away the need

for this kind of detailed molecular map of the metabolic maze. This solu

tion does not rely on such detailed understanding of what causes lysosomal

failure in atherosclerosis. Instead, it provides a way for us to clean up the

lysosome itself, rather than the metabolic processes that overload it—and

in a manner that will work irrespective of what leads up to its initial failure.

But before we get into that, let's look at another fearsome disease of ag

ing that has lysosomal dysfunction at its heart: the decay of the brain.

Neurodegenerative Disease

Except in the case of stroke—which I've covered above, and which is more

of a one-off, traumatic injury than a degenerative process in itself—the

brains of people suffering from all the major neurodegenerative diseases

show evidence of inadequate lysosomal function. In most cases, the most

obvious pointer is the presence of clumps of a distinctive aggregated pro

tein material inside the brain cell: Lewy bodies in Parkinson's disease and

the boldly named "Dementia with Lewy Bodies" (DLB), aggregated hunt-

U P G R A D I N G T H E B I O L O G I C A L I N C I N E R A T O R S 1 1 5

ingtin protein in Huntington's disease, and neurofibrillary tangles (NFT),

formed of aggregations of the protein tau, in Niemann-Pick and Alzheimer's

diseases. 1 0 Yet, because these aggregates are not located within the lyso

some, and are not themselves lipofuscin, the role of lysosomal dysfunction

in these diseases has been obscured—so again, people specifically looking

for a connection with "lipofuscin" can miss these data, obscuring the rela

tionship.

In several cases, however, there is more direct evidence of trouble at

the toxic waste dump. Some of the most remarkable such evidence has re

cently been found in the brains of Alzheimer's patients, in which the break

down of proteins through another of the main components of the cell's

recycling system (the proteasome) is badly impaired. In some victims, this

may be because mutations in the gene for a protein called ubiquilin cause it

to inhibit the activity of ubiquitin, a protein that "tags" proteins for break

down in the proteasome. Both neurofibrillary tangles in Alzheimer's and

Lewy bodies in Parkinson's disease are loaded with ubiquitin, yet the pro

teasome system seems incapable of picking these aggregated materials up.

The connection with the lysosomal apparatus is this: proteasomes that

are not doing their job put more pressure on the lysosomal system as the

defective proteasomes (and the material they have failed to destroy) are

sent to the lysosome, increasing lipofuscin formation. 1 1 At least some of the

waste that the proteasome fails to pick up—along with damaged protea

some units themselves—is ultimately sent to the lysosomes: this phenome

non has been definitively observed in the case of aggregates normally

degraded by the proteasome in Huntington's disease, and is probably

what's responsible for the finding of a lot of ubiquitin inside the lysosomes

of the neurons of Alzheimer's patients.

But the most dramatic hallmarks of abnormal trash disposal in

Alzheimer's disease are the signs of malfunction in the lysosomal system it

self. As a bit of background: One of the main ways in which cellular rub-

bish gets delivered to the cellular recycling center is through a process

called "macroautophagy," in which the waste in question is swallowed

whole by a membrane structure called an autophagosome or autophagic vac

uole (AV), which then hooks up with the lysosome and fuses with it. (If this

term rings a bell, that's probably because I briefly mentioned it in Chapter

5 as the way in which damaged mitochondria are delivered to the lyso

some.) The result, in effect, is a bigger lysosome, with a single combined

membrane that surrounds both the contents of the AV and the hydrolytic

enzymes (and acidity) of the original lysosome to digest that contents.


Recent studies show that this aspect of lysosomal function is in a very

bad way in the brains of Alzheimer's victims. 1 2 It has been known for some

time that the lysosomal system in the Alzheimer's brain is, like the protea

some, apparently both hyperactivated and inactivated: it's as if the neuron

were an unthinking driver of a car with a worn-out engine, trying unsuc

cessfully to compensate for its misfiring cylinders by pushing down harder

on the gas pedal. The new work suggests one major reason why they fail:

Their brain cells-—and especially the cells located in areas of the brain that

are most badly affected by the disease—are full of multilayered AV-based

structures that are a lot like Russian nesting dolls, with one AV contained

within another, larger one, which in turn is sequestered inside another, still

larger AV.

Some of these structures seem to form when AVs fail to fuse with lyso

somes, and hang around in the cell long enough to begin to take some

damage, ultimately becoming so badly degraded as to be recognized as

junk—at which point they are swallowed up into another autophagic vac

uole. Then, the cycle repeats itself, as the new AV itself fails to fuse. In other

cases, it appears that the AVs have fused with a lysosome, but that the lyso

some is so weak—or perhaps so immature—that it can't degrade the AV

contents.

It's a picture that reminds me of nothing so much as the infamous

Khian Sea, a ship hired by the city of Pennsylvania in 1986 to haul its incin

erator ash to an artificial island in the Bahamas for disposal. Unfortunately,

the Bahamian government had not given the operators of the Khian Sea

permission to dump its waste there. And so began a fourteen-year world

cruise of garbage, in which the ship traveled from port to port, attempting

to dispose of its load in different countries all over the world—first back up

the east coast of the United States, then back down south to the Caribbean

and South America, and ultimately wandering as far afield as Indonesia and

the Philippines.

Ultimately, the Khian Sea—renamed and reflagged—relieved itself of

its toxic burden by illegally dumping it into the Atlantic and Indian

Oceans. Sooner or later, peripatetic AVs can only be expected to discharge

their hazardous contents, too.

Scientists all agree about the basic facts: the major neurodegenerative

diseases are characterised by the presence of aggregated proteins and lyso

somal dysfunction in the brain, and it's clear to everyone involved that

there is some kind of connection between the clear failure of the cell's waste

disposal systems to deal with the aggregates and the diseases in which these


disruptions occur. The question is just what that connection is. Intuitively,

it makes sense that the aggregated junk sitting around in our brain cells

must be bad for them. Most scientists in the field share this intuition, and

indeed it's easy to show, in relatively crude test-tube experiments, that these

substances work mischief in brain cells to which they are added, including

the initiation of a vicious cycle in which the accumulation of aggregates dis

rupts normal neuronal function, leading to further lysosomal dysfunction

and protein aggregation.

But others have a different take on these phenomena. Surprisingly,

some scientists think that protein aggregates may in some sense be protec

tive. The idea is that while the aggregates themselves may in the long term

interfere with cell function by blocking cellular traffic with their sheer size,

the soluble, highly reactive units that make up the aggregate are a much

more immediate threat to the health of the cell. By handcuffing these units

together into a single cellular chain gang, the cell can keep them from at

tacking other cellular apparatus in their environment, preventing a deadly

short-term threat to cellular health.

And then there are those who view the aggregates as being more of an

epiphenomenon: a sign that something is wrong with the cell, but not an

actual contributor to pathology. In this model, undegraded protein de

posits are more like gunsmoke than actual guns or the bullets they fire: in

themselves they are more-or-less harmless, but their presence is an unmis-

takeable signal that you're in a crime scene. Perhaps, for instance, some

other contaminant is building up in the lysosome, preventing it from prop

erly incinerating cellular garbage, so that the aggregates build up—but the

aggregates themselves aren't the source of the problem or a major contribu

tor to cellular pathology. This is still a bad thing to have happening, of

course, because cells rely on a functional lysosome—both to break down

benign cellular constituents that are past their useful life in order to make

use of their building blocks for future cellular construction projects, and to

destroy genuinely toxic wastes. But the source of the problem is to be

found elsewhere than the obvious piles of trash cluttering about the main

body of the cell.

For example, Alzheimer's patients may have more defective mitochon

dria in need of recycling than healthy people do, putting demands on the

lysosome that it just can't satisfy; once the lysosome fails, other components

may form the observed aggregates, but it's still the dysfunctional mitochon

dria that started the ball rolling downhill. But again, it's pretty hard to es

cape the conclusion that the resulting protein clumps constitute cellular


"speed bumps" that must eventually cause the cell some serious problems

of their own.

Unfortunately, there is substantial evidence—both in neurodegenera

tive disease and in aging—to support each of these positions. "Unfortu

nately," I say, because I feel it is paralysing researchers in their quest for

cures. Researchers spent much of the 1990s in entrenched holy wars be

tween the "BAPtists" (named for "Beta-Amyloid Protein") and the

"Tauists" (named for the tau-based neurofibrillary tangles or NFTs), each

of which expended considerable effort in trying to prove their favored can

didate to be the primary problem in Alzheimer's disease. ("What's beta-

amyloid?" I hear you cry. You'll learn plenty about that in Chapter 8.)

Today, there is a similar feud simmering over the different interpretations

of the role of protein aggregates generally in neurodegenerative disease.

And in old-school thinking—in which the goal is to find drugs that will

shut down the metabolic processes that lead to a disease outcome, or at

least perturb that aspect of the pathway that causes the most harm—issues

of this kind must be definitively resolved in detail before we can even begin

to design treatments for humans, since interfering with metabolic pathways

is a risky business that can only lead to harm if the process that you're

blocking turns out to be an innocent bystander.

Even more so than with atherosclerosis, then, traditional medical ap

proaches to neurodegenerative disease are, with respect to protein aggre

gates, at a standstill because of inadequate understanding of the link

between the junk in question and the disease itself.1 3 Again, however, I have

a solution in mind that sweeps aside the need to resolve these ambiguities.

Macular Degeneration

While I don't wish to tease you, I do want to go over the critical role of unde

graded aggregates in a third important aspect of aging before finally revealing

my proposed therapy for all diseases involving lysosomal failure—including

aging itself. This third age-related problem is age-related macular degenera

tion (AMD).

There is some relief from suspense in this section, inasmuch as there is

no controversy about the involvement of aggregates in AMD. This is a clas

sic case of how biochemical cycles with which we absolutely cannot dis

pense lead to the destruction of the systems in which they are embedded.

Vision, like all of life's processes, is ultimately mediated by a carefully con-


trolled, complex chemical chain reaction, and our conscious perceptions

correspond in a one-to-one fashion with the particular electrochemical

phenomena that this cascade triggers in our brains. In order to perceive an

object, the energy from the light that reflects off it and into the lens of our

eyes must be translated into the chemical signalling language that corre

sponds to our subjective "sight" of the object.

For our purposes, the important step in this translation process—

important because fatal to the cells that suffer it, and hence to our eyesight—

is the (nearly) perpetual cycle of a derivative of vitamin A between two

forms.14 The rods and cones of your eyes contain the "storage" form of this

compound (ll-cis-retinal), which is chemically transformed into an "acti

vated" derivative (all-trans-retinal) when it absorbs energy from incoming

light. This activated form is used as a signal to turn on the electrochemical fir

ing of the optic nerve, which carries the signal to your brain; then, normally,

an enzyme converts it back into its "storage" form, readying it for the next

burst of incoming light.

But any system that relies on chemically unstable components always

runs the risk that their reactive chemistry will spill over the tight controls of

the system they're meant to serve. In this case, all-trans-retinal can react

with some of the fatlike molecules that make up the cell membrane, lead

ing through a complex series of steps to the formation of a stubborn end

product called A2E. This compound is completely resistant to digestion

within the lysosome, so it's a major source of undegraded junk in the lyso

somes of these cells. Over time, so much A2E is p r o d u c e d and absorbed

into the lysosome without being degraded that it can take up as much as

one fifth of the total cell volume in the cells that accumulate it. These un

fortunate cells make up the retinal pigmented epithelium (RPE) of the

eye—a part responsible for maintaining the function of the light-sensing ar

eas of the retina.

But again, because of the specialist terminology in use (A2E, rather

than "lipofuscin"), the role of lysosomal inadequacy has been—and you

will pardon the unfortunate pun!—obscured .

Toxic Waste Problem—Toxic Waste Solution

By the morning that I was throwing some clothes into a duffel bag for the

1999 Society for Free Radical Research meeting in Dresden, I had come to

see lysosomal inadequacy—and the resulting accumulation of cellular


waste products—as perhaps the key step linking the mitochondrial

mutation-driven rise in oxidative stress with age with the actual pathology

of aging. Remember from Chapter 5 that, by then, I had a scheme for how

mitochondrial mutations in a few cells could propagate toxins to mitochon

drially healthy cells elsewhere. What I didn't explain in Chapter 5, not least

because when I developed the Reductive Hotspot Hypothesis I didn't

know it, was just how these "toxins" are toxic—what harm they might do

to the cells that ingest them.

But now, a year later, this mystery was beginning to resolve. It was

clear, once one got over one's attachment to the term "lipofuscin," that the

failure to dispose of specific waste products was at the root of the most ter

rible diseases that accompany biological aging: atherosclerosis, age-related

macular degeneration, and neurodegenerative diseases like Alzheimer's. It

was just that the kind of waste that was linked to a given disease was specific

to the cell type and the particular diagnosis.

As it happened, Ulf Brunk was again presenting his data in Dresden.

As I listened to his talk and contemplated his slides—the telltale red glow

of lipofuscin choking cells, his computer-generated diagrams illustrating

his and Terman's "garbage catastrophe" theory—I saw that it was a waste

of time to argue about whether lipofuscin contributes to "aging" in the nar

row sense. Clearly, we needed a way to solve this problem if we were to pro

tect our bodies from age-related pathology. But I also became convinced

that it would not be enough to try to prevent the accumulation of this junk

"upstream" by obviating mitochondrial mutations. We were also going to

have to deal with the junk directly.

But how? With the recalcitrant materials in question being so multifar

ious, and with the metabolic pathways, chemical identities, and even spe

cific role in pathology of these materials being still largely unknown, it

seemed that no classic "magic bullet" approach—one small molecule to

match one therapeutic target—would work. And simply putting the lyso

some into overdrive wouldn't really solve the problem: While, as later ani

mal studies would show, 1 5 , 1 6 simply souping up lysosomal activity or

topping up their existing enzyme supply could slow down the progression

of lysosomal storage diseases, such approaches could not ultimately stop

those diseases. It is the very nature of the problem that the body simply

does not have the enzymes to degrade the really ugly junk—and thus, that it

will choke up your cells, steal your mind, blind you, and clog your arteries

later, if not sooner.

Ulf's talk ended, and with a hundred other scientists I got up and


streamed into the outer hall for the coffee break. The red glow of lipofuscin

on the slides had gotten me to thinking of the stuff as the toxic waste that it

is, and of the aging cell as a tiny contaminated environmental site equipped

with a woefully inadequate waste management system. So the job of restor

ing the cell to health was really a kind of environmental cleanup job, and

what was needed was a biomedical superfund project to develop new reme

diation technologies capable of dealing with materials that had so far

evaded the lysosome's capacities.

Superfund!

It suddenly occurred to me that this was more than a metaphor. (If

you've never heard of Superfund, be patient—I'll explain shortly.) There

were actual land sites all over the planet that should be very badly contami

nated by lipofuscin, because their soil has been seeded with the stuff for

generations. I speak, of course, of graveyards. Think about it: hundreds of

bodies put into the ground—sometimes en masse, as happened throughout

Europe during the horrors of the Plague, and more recently following acts

of genocide in Rwanda and elsewhere. These soils should be chockablock

with aggregates from their inhabitants' decaying bodies.

Yet, to my knowledge, there was no accumulation of lipofuscin in

cemeteries—and if there were, we certainly ought to be aware of it, because

lipofuscin is fluorescent. Months later, when I was discussing the issue with

fellow Cambridge scientist John Archer, he would put the disconnect suc

cinctly: "Why don't graveyards glow in the dark?"

Soil microorganisms struck me as the most likely explanation. Bacteria,

fungi, and other microbes normally play a role in turning our remains into

compost, of course, but it was not so immediately obvious that they would

be able to digest something so resistant to enzymatic action as lipofuscin.

And yet, I recalled, we'd known for decades that soil microbes display an

astonishing diversity in their choice of food.

Scientists became interested in this phenomenon in the 1950s, when it

was noted that the levels of many hard-to-degrade pollutants at contami

nated sites were present at much lower levels than would have been ex

pected. A big part of the explanation turned out to be the rapid evolution

of quickly reproducing organisms like bacteria. Any highly energy-rich

substance represents a potential feast—and thus, an ecological niche—for

any organism possessing the enzymes needed to digest that material and

liberate its stored energy. The presence of high levels of such a material

therefore creates a powerful evolutionary "pull," driving the evolution of

the necessary enzymes in microorganisms that come into contact with it.


And this is especially so if the substance is not easy to break down, because

then the chances are good that most of the other organisms in the vicinity

will not have enzymes capable of this degradation.

It was proposed in 1952 that these forces might well be so strong as to

guarantee that, given enough time, evolution would find a way to create mi

crobes with the capacity to digest anything we throw at them that is both

carbon-based and rich enough in energy to be a worthwhile fuel source.

This was given the immensely memorable name "the microbial infallibility

hypothesis." While it has turned out to be a bit of an overstatement—no

one has yet discovered the microorganism that can eat Teflon, for instance—

studies over the next few decades tended to confirm the general principle.

U.S. Geological Survey scientists collected case studies showing that mi

croorganisms were breaking down significant amounts of a variety of or

ganic chemical pollutants in wastewater. Oil spills, chlorinated solvents,

pesticides—you name it: soil bacteria learned how to digest almost any

thing that was thrown at them, leaving only harmless residues like carbon

dioxide and water.

Scientists' first attempts to harness this power failed, because they were

trying to invent organisms to order, imitating what nature was already do

ing very well. But eventually, researchers realized that they just weren't as

smart (nor, more accurately, as fast) as the forces of nature. Out of these ob

servations developed bioremediation: the exploitation of evolution's ability

to generate novel digestive capacities in microorganisms for the intentional

cleanup of contaminated environments. "Superfund" was the name of a

U.S. government initiative to stimulate and commercialize bioremediation

research.

Sipping my coffee in Dresden, my mind brought this train of thought

full circle, feeding back into my original musing on the lysosome as an in

adequate toxic waste disposal system. The lysosome already deals with the

cell's waste products using enzymes to break them down into their con

stituents. But it is not equipped with the capacity to deal with every possible

waste material. This is just what you'd expect from evolutionary theory. Re

member, again, as we discussed in Chapter 3, that evolution only designs

your body to last as long as your environmental niche will allow it to last. In

the Paleolithic environment in which we evolved, that meant about three

decades—far less time than it takes lipofuscin or atherosclerotic cholesterol

aggregates to build up to life-threatening levels.

For this reason, evolution has never bothered to equip the lysosome

with enzymes designed to deal with these wastes, because it has never had


a good reason to do so. But, as we've seen, it seems very likely that evolu

tionary forces have pushed soil microorganisms to develop these capacities

in order to exploit a new fuel source—an issue, for them, of day-to-day sur

vival. Not only do evolutionary theory and the "microbial infallibility hy

pothesis" predict this, but it also seems to be confirmed by the absence of

large accumulations of lipofuscin in mass grave sites: were it not so, all such

locations would have an eerie glow about them, instead of such a phenom

enon being confined to cheesy horror flicks.

Suddenly it came together. The imaginative spark of metaphor had

fallen upon the very concrete fuel of data in the oxygen-rich environment

of evolutionary theory, and a fire began to burn in my brain. These two ob

servations implied that we could perform a sort of medical bioremediation,

in which we would identify the soil bacteria that already clean up our un

degraded junk after we have died, determine the enzymes that allow them

to do it—and then deliver these enzymes into the lysosomes of people who

were still alive to benefit from it. Figure 1 gives a graphical depiction of this

cycle.

These enzymes would give new powers to our cellular recycling centers,

allowing them to process materials that presently go undegraded within us—

not just preventing, but reversing their pathological accumulation. Our

brains would be cleared of neurofibrillary tangles; the dying macrophages in

our arteries would gain new life, letting them clear out the oxidized LDL tox

ins and allowing the necrotic vessel tissue to finally heal; the blind would see.

And aging cells all over our bodies, choking on their own filth, would be

come clean and new again.

Figure 1. Medical bioremediation, exploiting the microbial enzymes that turn dead people into decomposed people, may retard many of the processes that turn young people into old and eventually dead people in the first place.


Normally, when new ideas come to me, I give myself a few days to try to

punch holes in them before bouncing them off anyone else. But this time I

felt supremely confident. Taking my nose out of my coffee, I scanned the

hall for Dr. Brunk. I spotted him across the room: chubby, graying, earnest

but with a mien of compassion that made you think of him as an aging so

cial crusader. In a few purposeful strides I was confronting him.

"Listen, Ulf," I said quickly, "I've just had the most fabulous idea . . ."

A Quick-and-Dirty Test

I was a little disappointed by Brunk's reaction, though I was not sure how

much of what I was seeing was a reflection of his assessment of the feasibil

ity of the entire scheme versus its inherent audacity or my jumbled, hot-

off-the-fire delivery. Perhaps it was just Nordic caution. Whatever it was, it

was clear that, while not dismissive of the proposal, Brunk was clearly not

experiencing spontaneous combustion from the white heat of my brain

wave.

Still, I pressed him for his thoughts on possible ways to perform pre

liminary tests of the idea. The first thing, we agreed, would be to test the

sturdiness of the very foundation of the castle that I had just constructed in

the air: the idea that soil microorganisms are, indeed, routinely digesting

lipofuscin in corpses. Fortunately, there was a reasonably straightforward

way to execute such a test: collect some soil microorganisms from a site

likely to be "enriched" in human remains, and then see if they could break

down lipofuscin in a test tube.

It turned out that what you might think to be the easy part—getting

the lipofuscin needed to test the abilities of graveyard bacteria—was actu

ally almost impossible to pull off in the real world. There are only small

amounts of lipofuscin in most of our cells, and the tissues in which there's

more (such as the heart) are not so readily available, so to get a useful

quantity of the stuff would be a challenge. But Brunk said that he could

whip me up a batch of an excellent substitute: the synthetic lipofuscin

used by people working in his field, which is created by merely exposing

mitochondria to enough ultraviolet radiation to induce cross-linking of

their membrane proteins. The resulting recalcitrant gunk has the same flu

orescence spectrum as the real thing, and seems to also have the same

physical and chemical properties—which is as you'd expect, since most

experts think lipofuscin largely is the remains of unsuccessfully degraded


mitochondria, damaged by the effects of free radicals and left festering in

the lysosome.

The next thing would be to gather microorganisms from soil that had

been exposed to a large supply of lipofuscin, to look for the ones that, in

my hypothesis, had been responsible for breaking the stuff down. My mind

had already leapt ahead to the fact that John Archer—the man who would

later make the "glowing graveyard" quip—was working on bioremediation

at Cambridge. As such, he was well-versed in the techniques used by scien

tists in the industry to isolate and culture bacterial strains capable of di

gesting classical toxic waste materials, and to identify and clone the

genes involved in producing the enzymes responsible for that capacity. If I

could enlist his help, we could do the same thing for lipofuscin-digesting

hydrolases.

Tomb Raider

Fortunately, John was immediately fascinated by the whole idea, and agreed

to give it a go. So it was that his graduate student would find herself, like a

good mad scientist, at Midsummer Common in the twilight of a late sum

mer day, digging into the soil of an ancient mass grave with a trowel, seek

ing not bodies but tiny, mysterious creatures imbued with the power to

turn the most stubborn, aggregated junk in our bodies into compost.

The sense of being immersed in a Gothic horror novella lasted only a

moment. Having scooped up the soil and brought it back to the lab, John

and his student isolated the microbes and put them in petri dishes with the

synthetic lipofuscin as their only potential food supply. Then, we waited to

see if the force of natural selection would reveal the existence of strains that

were capable of surviving on a diet of pure lipofuscin.

Almost immediately, the microbes that we had isolated began to give

off the characteristic red glow of lipofuscin under the fluorescing light of

the specialized microscopes. This was not yet a success, because all it meant

was that the microbes were engulfing the material; they weren't necessarily

digesting it. But it was not long before clear differences began to emerge

among different strains. Most of the colonies of microbes were in a state of

growth arrest, failing to thrive for lack of nourishment. But a few of them

were clearly enjoying a ghoulish feast: their numbers were expanding rap

idly as their hydrolytic enzymes slowly broke the stubborn goo down into

usable components, tearing apart its complex organic chemical bonds to

1 2 6 E N D I N G A G I N G

release the stored energy. Within short order, we had a sample of microor

ganisms equipped with enzymes that could digest lipofuscin in the same

way that the enzymes in your stomach digest a steak.

The hypothesis had been confirmed. The next challenge would be to

move those enzymes into our own lysosomes. No one has done this yet, and

indeed there is a sense in which the task sits just where it was when I fin

ished my work with John Archer. Fortunately, however, we do not have to

create an entirely new field of medicine in order to get going with this idea

(which I will from here on call "LysoSENS"). That's because the funda

mental biotechnology required to pull it off is already in clinical use. Pio

neering physicians have been introducing "foreign" lysosomal enzymes

into patients for several years—not in aging, but in the lysosomal storage

diseases.

Cleaning Out the Drain

Lysosomal storage diseases, the syndromes that we now know to be the re

sult of mutations in genes that code for our normal complement of lysoso

mal enzymes, had been known for decades before researchers figured out

what was causing them. Once their origins became clear, however, a way to

treat most LSDs became apparent: enzyme replacement therapy (ERT—

don't confuse the abbreviation with estrogen replacement therapy). In indi

viduals lacking an enzyme for some common metabolic waste, undegraded

cellular waste products build up within the lysosome (and also outside it in

the main body of the cell), and cellular dysfunction inevitably results.

Therefore, it was reasoned, if the right enzyme could be delivered to the

lysosome, the cellular recycling center would return to normal function, the

piled-up garbage would be broken down, cells would return to health, and

victims would be able to lead normal lives.

After a few decades of work, victims of three of the most common

LSDs are now being successfully treated with such therapies. There are, for

instance, about four thousand people now living normal lives despite hav

ing Gaucher's disease, thanks to regular injections of the lysosomal enzyme

that their cells are unable to produce for themselves. The drug develop

ment process has been reasonably clear, although technically challenging.

In one disease after another, scientists have identified the enzyme whose

absence causes the disorder; modified it in various ways to allow it to be in

jected, taken up by cells, and delivered to the patient's lysosome, where


they function exactly like the same enzyme does in the rest of us when it is

produced by our own cells; and watched as symptoms have disappeared,

lives have been extended, and victims have been enabled to live the life that

the rest of us take for granted.

Of course, the same fundamental problem faces all of us in the case of

diseases of long-term lysosomal failure: we will all ultimately suffer from

age-related "lysosomal storage diseases" (such as age-related neurodegener

ative disease, macular degeneration, and atherosclerosis), even though only

a tiny proportion of the population is stricken with the currently recog

nized congenital ones (Gaucher's disease and the like). While the exact ori

gins of the two kinds of LSDs are different (rare genetic mutations in genes

for lysosomal hydrolases that are otherwise part of the species' standard

evolutionary legacy in the congenital LSDs, versus never having evolved

the enzymes needed to break down neurofibrillary tangles, A2E, etc., in the

age-related diseases), the molecular natures of both congenital and age-

related LSDs are essentially the same—and as anti-aging bioengineers, that

is quite sufficient to let us do our job, which is to clean out the accumulat

ing molecular damage. To arrive at that destination, we will need to address

a series of specific challenges. Fortunately, in all cases we have options

available with which we already have experience, or for which the solutions

are clearly in sight and under development by researchers in other fields of

biomedicine.

First Challenge: Identifying Suitable Enzymes

Our "grave robber" raid on Midsummer Common proved that the en

zymes exist to degrade the highly cross-linked remains of mitochondria—

believed to be the single largest contributor to lipofuscin. However, we still

don't know exactly what enzyme or series of enzymes is doing the job.

Moreover, enzymes that degrade this synthetic lipofuscin will not be enough:

we also need to identify other enzymes that will deal with wastes clogging

up lysosomes in a variety of tissues and associated with various disease

states.

This doesn't necessarily mean enzymes that will degrade any known

aggregate, such as neurofibrillary tangles. As we discussed above, the messes

that we see are not necessarily the ones causing the problems: they may be

the gunsmoke rather than the gun itself. For instance, it's possible that

some other junk is actually responsible for backing up the system, and thus


that the aggregates that pile up like so much trash in the street are simply

what results when the lysosome can't keep up with its normal load. In fact,

the problem might not even be the presence of undegradable materials: in

several diseases, some researchers have presented evidence to suggest that

the problem is a substance (for instance, A2E in macular degeneration) that

directly inhibits the activity of the pump responsible for keeping lysosomes

acidic enough for their enzymes to work.

Fortunately, we again don't need to trouble ourselves with this. Once

again, our job is not to tease apart the minutiae of metabolism, but to clean

up age-related damage. To do that, we can follow the example of the biore

mediation experts: throw enzymes at the problem until the problem is

solved (normal lysosomal function is restored), and then identify the en

zyme that did it. That's a simple task in principle—but when the bioreme

diation field first got going thirty years ago, it was a long slog to actually

narrow down which of hundreds of enzymes in a strain of microorganisms

were responsible for breaking down the wastes of interest.

One of my reasons for optimism, therefore, is the fact that so much

progress was made in those days—and today, we have much more sophisti

cated molecular tools available to do the job. One is a method called mo

lecular fingerprinting, but that term is a little bit misleading. It suggests

a process of finding a clear, unique identifier of an individual—like a

fingerprint—and then finding the individual that bears that same identifier.

Instead, molecular fingerprinting is based on the fact that the members of a

closely knit family of organisms tend to carry genes with broadly similar se

quences, and that (similarly) genes for a range of enzymes with broadly

similar functions within such a community also tend to have a similar

stretches of code.

This allows us to winnow our way down to the genes (and, therefore,

enzymes) of interest from either of two angles. One option is to focus on a

class of enzymes for whose encoding genes we are searching (in this case,

hydrolase enzymes), and then to look for genes that match the overall pat

tern and are expressed in large amounts when the parent organism is feast

ing on the contents of the dysfunctional lysosomes. The other option is to

identify, within a community of organisms, which specific ones are thriving

best when only given those contents as nourishment—and which therefore

carry the genes encoding those enzymes most effectively tearing their

contents down.

Another powerful tool at our disposal is DNA microarrays, or gene

chips. These are tools that identify, in real time, which genes in an organism


are being actively expressed at a given moment. So, if we can isolate strains

that are doing well on a diet of lysosomal detritus, we can sequence their

genetic libraries, and then test which of those genes are being used inten

sively when they are feasting on the stuff.

We can also use techniques that allow us to "knock out" (simply re

move) specific genes in such strains, and then retest them. When we knock

out a given gene in a strain of microbe and see that the mutants starve on a

diet that was previously their version of a gourmand's wet dream, we can in

fer that the gene in question encodes a protein that is critical to the se

quence of processes involved in digesting such materials. We can then

identify these genes, and see whether the enzymes they encode are the cru

cial ones that will fill in the weak spot in our human hydrolytic arsenal.

Second Challenge: Getting Them to the Cells

Once we have enzymes in hand that will do the job, we'll have to find ways

of getting them into the cells that need them. Not every cell type will be con

fronted with the same kinds of waste: as we've seen above, particular disease

states are characterized by specific aggregated waste products, and (as is es

pecially likely in the case of A2E in macular degeneration) this is the result

of the particular metabolic pathways that produces them. How much we

have to do to address this challenge will depend on exactly how we're going

to get them into the body at all—for which there are again multiple options.

Right now, for instance, doctors treat L S D patients by intravenously in

jecting modified forms of their missing lysosomal enzyme. Of course, the

enzyme does the patient no good when it's just floating around in the

bloodstream, and it might even do some harm if it were active (since it

might start attacking functional proteins), so the enzymes are tweaked in

ways to ensure that they go where they're needed. First, they are targeted to

the right cells. In Gaucher's disease, for instance, macrophages are espe

cially vulnerable to the lack of the enzyme that causes the disease. There

fore, the enzyme is hitched to targeting molecules that are already recognised

by macrophages as passports to entry. The same trick might, therefore, be

used to target enzymes needed to clear away the substances that cause

macrophage lysosomes to fail in atherosclerosis.

This method has the advantage of being relatively simple to implement

in the short term, and indeed of already being in use for a recognized dis

ease (so that we have a large body of practical, clinical experience with the


basic technique on which to draw). It does, however, face a variety of limi

tations. Most notably, there's a big difficulty in using it to move enzymes

past the protective blood-brain barrier, which is a highly effective shield de

signed to guard your brain against exposure to the many potentially toxic

substances floating around in your blood. Obviously, injecting enzymes that

cannot reach the brain will seriously limit their benefits—and represents an

almost complete barrier against their use for age-related neurodegenerative

disease. Even today, some Gaucher's patients develop neurological compli

cations as a result of their enzyme deficiency, and injected hydrolases are of

little help to such patients.

Fortunately, scientists are making progress in coming up with ways to

move proteins across the blood-brain barrier—and in the future, we can ex

pect to have much more powerful delivery systems. In the relatively short

term, we should be able to develop a form of cell therapy, involving seeding

the patient with cells that produce the needed enzyme and secrete it into the

bloodstream or into the fluid bathing surrounding cells. 1 7 This would there

fore act like a biological version of the nicotine patch, providing a continuous

dose of the enzyme. This might be extremely useful: right now, LSD victims

rely on regular injections of heroic amounts of their needed enzyme, and it's

possible that the sheer quantity of (several) enzymes required to combat all

types of lysosomal failure due to aging or age-associated disease might make

injection impractical. One reason why so much enzyme is needed is that

some of these enzymes are proteases—that's to say, they break down

proteins—but enzymes are proteins, so proteases in the lysosome actually de

stroy themselves and each other.

And, of course, the ideal would be to modify our own cells using so

matic gene therapy, introducing DNA to instruct the relevant cells to pro

duce the very enzymes that they need to stay healthy. This, and the cell

therapy option too, are still a long way away from the anti-aging clinic—but

again, fortunately, the major hurdles will be tackled first for a variety of

better-recognized diseases, from sickle cell anemia to the severe combined

immunodeficiency disease that creates "bubble babies." Thus, we can ex

pect to ride on their coattails to a certain extent. Indeed, once somatic gene

therapy is available for use in treating relatively common genetic disorders,

it will doubtless be seized upon by LSD researchers as a way to replace

genes for the lysosomal hydrolases missing in their patients. Again, the spe

cific use of gene therapy to provide better solutions for LSD victims will be

a useful source of information and collaboration to develop a gene therapy

version of the LysoSENS project.


Third Challenge: Getting Them to the Lysosome

This is similar to the second challenge, above: lysosomal enzymes do us no

good—and might conceivably even cause us some problems—if they wind

up (or, in the case of gene therapy, are synthesized) inside the cells where

they're needed but are not then localized in the lysosome where the junk

accumulates and where the acidity is available to let them do their work.

Again, one potential solution is already in use in the LSDs: the use of mol

ecules of the sugar mannose 6-phosphate, which is recognized and taken

up—along with its cargo—by the lysosome.

But again, we are also in the process of learning to hide a few other

cards in our sleeves. We might be able to use a backdoor solution, by turn

ing a targeting system that is currently used to ensure wastes get delivered

to the lysosome into a method of sending enzymes into the heart of the same

system. (This system is called chaperone-mediated autophagy.) Lysosomes

would take the enzyme up just as if it were any of numerous classes of cel

lular detritus, but would instead incorporate a hydrolase capable of pre

serving and restoring its normal functioning.

We might also be able to take advantage of targeting systems already in

use in the organism from which we originally isolated the enzymes in ques

tion. Bioremediation typically uses bacteria as the microorganism of choice

because they digest their food quickly. Fungi, by contrast, are usually viewed

as too slow-acting and slow-growing to provide viable solutions for oil slicks

or contaminated chemical spill sites. But in a slowly accumulating, low-

volume toxic waste problem like age-related lysosomal failure, these issues

would be less of a problem. The advantage of using fungi is that they—like

us, and unlike bacteria—have a lysosome-like structure of their own, called

the vacuole, which shares many of the key characteristics of the human

equivalent (including, for instance, the need for an acidic internal milieu to

work properly). Enzymes taken from such sources, then, might come al

ready equipped with a range of features that would be useful for the

LysoSENS project in humans.

Fourth Challenge: Potential Side Effects

Even once we have ways to deliver useful enzymes to the lysosomes of af

fected cells, we will still face the key challenge of preventing the interven

tion itself from causing us harm. One potential issue is that the enzymes in


question might, as suggested earlier, also be active elsewhere than in the

lysosome. One reason to expect that this won't pose a major challenge is

the fact that, as already mentioned a few times, lysosomal enzymes typically

require a very acidic environment to function properly, so they will proba

bly be nearly inactive in the main body of the cell.

We might also, however, further modify the enzyme so that it only be

comes active after it has been taken up by the lysosome. One possible such

modification would be to attach an extended sequence of amino acids that

would prevent the enzyme from being active, but that would be cleaved off

by enzymes present and active in the lysosome, liberating the active form

for duty at its destination. This concept sounds really tricky, but it is already

used by the cell for the safe delivery of some members of the standard hu

man lysosomal enzyme complement, so the technique should be adaptable

without overmuch heroics.

Another potential worry is that the enzyme might cause an immune re

action, just as any "foreign" protein might. But experience with the LSDs

suggests that this will not be as big a problem as one might at first expect.

Remember that, for a person who was born unable to produce the hy-

drolytic enzymes that the rest of us take for granted, these proteins are

every bit as "foreign" as the microbial hydrolases will be to all of us. Nor

mally, we learn to be tolerant of the proteins of our own bodies because our

immune system is exposed to them early on in our prenatal and childhood

development, allowing it to recognize them as "self." Having never been

exposed to such proteins in early life (because without the gene, the pro

tein can't be constructed), LSD victims lack immune tolerance to them.

And in such patients, immune reactions do occur. But, reassuringly, they

are always mild, and they taper off with time. This seems to be because en

zyme replacement therapy delivers enzymes to the lysosome in a way that

does not allow the cell to hack them up and to display them on its cell sur

face, alerting a suspicious immune system to their presence.

Moreover, even if the experience with the newly introduced enzymes is

not the same (for instance, if we find reasons to use gene therapy and

chaperone-mediated autophagy rather than ERT), we aren't necessarily

stuck. Dampening down an excessive immune response is a necessary part

of many medical procedures, from organ transplants to over-the-counter

allergy medications, and we are getting better at it all the time. We might

also eventually be able to produce the protein within the bone marrow, as

has already been done with some lysosomal enzymes; this might also help

to induce tolerance, because of the role of bone marrow cells in immunity.


Inside, Outside

As you can see, there are quite a few hurdles to be overcome before we will

be able to use novel hydrolytic enzymes to clear out the junk in our cells,

preventing or reversing many of the most debilitating health problems of

old age. But, as I've shown, perfectly plausible solutions to all of these

problems seem to exist that are either already in use in treating the recog

nized (congenital) LSDs, or else have clear routes to implementation that

are the subject of intense study by researchers the world over. Identify the

enzymes we need, and a first-generation therapy might look much like ERT

for lysosomal storage diseases today: expensive, inconvenient, and limited

in its scope, but lifesaving. And as we go on, we will progressively improve

the therapy, making it more comprehensive and advancing its safety and ef

ficiency in lockstep with the advance of gene therapy and other enabling

technologies that will also be exploitable in LSD treatment.

As in previous cases, the pursuit of this solution will depend on an inter

disciplinary synthesis of research performed in areas that have, ostensibly, lit

tle to do with aging, and original work done by scientists dedicated to the

goal of adapting existing technologies to the novel problems associated with

the aging process. What is clearly needed is to get private and public capital

devoted to the latter half of the equation, which suffers from a serious lack of

investment of dollars and brainpower, and without which the greatest killer

of all in the modern world will continue to cripple, torture, and kill our fellow

human beings in enormous new cohorts every day.

Let me now turn from the junk within our cells to some of the aggre

gated junk coating our cells, exploring how it is harmful, what can be done

about it, and how its threats to your health—and its therapeutic solutions—

are intimately tied up with the lysosomal failure problem that we've been

exploring here.

C u t t i n g F r e e o f t h e C e l l u l a r

S p i d e r W e b s

Our cells—and thus our bodies—are progressively damaged

by protein-derived junk that gathers over the years in the

space between cells. Alzheimer's disease is perhaps the best-

known condition associated with this, but there are others that

are equally fatal. However, there is a way forward for medical

science and our health: recent and very promising research demon

strates that science can turn our own immune systems against

this dangerous material.

In the previous chapter, I talked about the junk that accumulates

inside our cells with age—how it contributes to the biological aging pro

cess, and what can be done to get rid of it. In this chapter, the focus is on

the garbage that accumulates on the outside of our cells and tissues, en

meshing them in webs of damaged proteins, impairing their function, and

contributing to aging and age-related disease.

Most of the junk that we'll be discussing is amyloid of one kind or an

other. When I say "amyloid," of course, almost everyone thinks of beta-

amyloid protein (also called "amyloid beta"), which accumulates as the

waxy "senile plaques" that cluster around the brain cells of people with

Alzheimer's disease. But many other, less-well-known diseases (amyloi-

doses) are also rooted in abnormal protein aggregates of this type. Most

8

C U T T I N G F R E E O F T H E C E L L U L A R S P I D E R W E B S 135

amyloids are cell-snaring chains of molecules that begin their existence as

healthy proteins already present naturally in our blood, or in the fluid

bathing our brains. A wide range of proteins can become amyloids under

the wrong circumstances, including immunoglobulin light chain, a key com

ponent of the antibodies in your immune system; the protein transthyretin,

which is responsible for carrying around thyroid hormones in your blood;

and a small protein (islet amyloid polypeptide, or IAPP—also referred to as

amylin) that helps your body regulate its blood sugar levels in association

with insulin.

What turns these proteins into snares that squeeze the life out of cells

and organs is how they are folded. Misfolded proteins are just what they

sound like: proteins that have become twisted out of their proper configura

tion in ways that cause them to undergo toxic interactions with each other, or

with other constituents of the cell. The ones that cause amyloid diseases con

tain sites within their structure that, if exposed, readily stick to other proteins

of the same sort, causing them to link together one after another in a sinister,

self-assembling daisy chain. These sticky sites are normally kept safely tucked

away within the complex folding of the protein's three-dimensional architec

ture, precisely to prevent such interactions from happening. Misfolding ex

poses such sites, initiating the spinning of a cell-choking web.

Many of the amyloid diseases result from the victims having faulty genes

that produce defective versions of these proteins. In some such disorders,

the underlying mutation introduces fatal flaws into the structure of the pro

tein itself, causing it to open up at inappropriate locations, exposing the crit

ical "sticky" site in its structure. Others involve mutations in enzymes that

normally chop up the protein into functional units as it emerges from the

cell's protein-assembly machinery. These mutations cause the enzymes to

cut too close to the critical site, again unleashing it from the restraining in

fluence of the rest of the protein's normal conformation. Another route to

congenital amyloidosis is errors in "chaperone" proteins whose job it is to

direct the emerging (and potentially amyloidogenic) protein to assume a

safe, nonamyloidogenic final shape.

But in addition to these inherited protein-misfolding diseases, there are

also universal amyloidoses—ones that are the result not of mutations, but

of the fundamental vulnerabilities that proteins face in the course of their

critical jobs in the molecular maelstrom of cellular biochemistry. With free

radicals, sugars (sugars? Oh yes. See Chapter 9) and vibration constantly

acting on them, proteins are bound to get bent out of shape now and again

in ways that open them up to becoming the seed of an amyloid fibril. Once


one such protein is formed, it can sometimes twist other proteins out of

shape as it grabs at them, exposing another site and forming the nucleus of

an ever-expanding fibril chain. One example of this happening in fast-

forward is seen in people with kidney failure, when the body ceases to pass

out beta-2-microglobulin in the urine. Beta-2-microglobulin is normally a

perfectly safe protein that helps the body to distinguish its own cells as

"self" from "nonself" cells of bacteria or other organisms. But without reg

ular excretion, levels of this protein begin to climb to abnormal levels, and

they eventually reach so high a concentration that they start to sponta

neously glom together, forming amyloid deposits.

Indeed, Cambridge professor Chris Dobson, who has spent his academic

life looking into protein misfolding diseases, says that "conditions could be

found in which seemingly any protein could form amyloid fibrils [emphasis

mine] . . . although the propensity to form such structures under given cir

cumstances can vary greatly from one protein to another."1 Over time, these

fibrils build up to potentially pathological levels, coiling around our cells and

organs, choking them off like so much bindweed.

Mind-Forg'd Manacles

Most researchers now believe that the horrors of Alzheimer's disease can

mostly be traced to abnormal processing of an otherwise healthy molecule

called amyloid precursor protein (APP). Everyone's brain produces APP,

and it is required for some essential function in our bodies. Ironically, in

fact, properly processed APP actually appears to be required for many of

the key activities of healthy neurons, such as their ability to rewire them

selves in response to new learning and to grow out the branching "electric

cables" (neurites) that allow them to talk with one another.

When things go right, APP is produced in the main body of the cell

and then sent for further processing to alpha-secretase,2 a type of enzyme

called an endoprotease. The result is the creation of two molecules, one of

which remains in the membrane of the neuron's neurites, while the other is

released into the fluid inside the cell. APP cannot form the evil beta-

amyloid when it is processed by alpha-secretase. After this, one of the frag

ments is chopped further, by a distinct enzyme named gamma-secretase.

APP only become dangerous when, instead of being trimmed down by

alpha-secretase, it is mistakenly cut up by a different, but related, enzyme

called b e ta - s ec re ta se . 3 Beta-secretase, like APP, is not a villain: it has a proper


place in the cellular "factory," as part of another, distinct cellular assembly

line from the one that handles APP. In that assembly line, beta-secretase

makes essential trims in the structure of other proteins that bear some mo

lecular resemblance to APP itself. But if beta-secretase performs the same

action on APP, it chops it in the wrong place. This distorts the protein's

shape and creates a molecule with a totally different action within the cell.

It's as if beta-secretase were an overly helpful laborer who, while cross

ing the factory floor on the way back from lunch, had seen some APP lying

on a stopped assembly line and mistaken it for a part that he or she nor

mally works on. Seeing no alpha-secretase around, and presuming to know

what the half-finished product needs, beta-secretase steps in to do alpha-

secretase a favor by taking care of a little bit of its workload. After giving it

a few whacks of its molecular hammers, beta-secretase tosses the APP

fragment—now subtly misshapen—back onto the line, where it eventually

reaches gamma-secretase. And because gamma-secretase is a busy enzyme,

it's too caught up in its work to notice the change, and proceeds to splice

and dice the distorted APP fragment just as it would if alpha-secretase had

made the proper modifications. Beta-amyloid is the product of this mis

taken sequence—the sequential cleavage by beta- and gamma-secretase

rather than by alpha and gamma.

When processed appropriately, the middle APP component (between

the sites of cleavage of alpha- and gamma-secretase) assumes a shape simi

lar to a stretched-out coiled spring—a conformation called an alpha helix.

But thanks to beta-secretase's molecular meddling (and gamma-secretase's

unwitting cooperation), this fragment loses its normal shape—and, just as

would happen if you were accidentally to cut into a tightly drawn spring

with a pair of wire cutters, the improper slicing of APP causes the fragment

to jump backwards on itself, creating a shape more like a bent hairpin (a

beta-sheet) that gives beta-amyloid the fatal molecular stickiness that char

acterizes amyloid proteins.

Once released by gamma-secretase, individual fragments ( m o n o m e r s )

of beta-amyloid initially float free in the brain. But they soon come into

contact with other monomers, and their "stickiness" causes them to glom

together into larger—but at this stage still free-floating—units called

oligomers. These fibrous strands, in turn, get stuck to one another to form

still longer strands, which eventually grow so large and complex that they

can't stay dissolved in the brain's fluids, but precipitate out into the spaces

between neurons to form the notorious plaques. Under a microscope, these

mind-snaring webs can be seen extending to the neurons' caretaking support


staff (the glial cells), and down to the neurites (the wiring system that I

mentioned earlier).

Some people produce unusually large amounts of beta-amyloid be

cause they have inherited mutations that either cause their bodies to pro

duce too much of APP itself (thus increasing the odds that the problematic

enzymes will come across molecules of it and mistakenly hew their struc

ture), or else encode defective secretase enzymes that are not so good at do

ing their selective jobs as the more common varieties. But because everyone

has both APP and the enzymes that can sometimes turn it into beta-

amyloid, we all produce beta-amyloid, and given a constant output of the

stuff, some fraction of that amyloid precursor is bound to get snipped in

the wrong way now and again. Once that happens, it's only a matter of time

before enough of it builds up to form Alzheimer's-type plaques-—and in

deed, all of us have at least some plaque in our brains by the time we reach

late middle age.

Thus, like other aging damage, beta-amyloid plaques simply accumu

late over time, and it's reasonable to think that neurological impairment oc

curs when a critical threshold is reached. This is probably why most cases

of Alzheimer's disease are not inherited, but instead occur sporadically in

the population: the underlying biochemistry is just part of the kind of or

ganisms we are, living in the kind of universe that we do. Lifestyle risk fac

tors and most genetic predispositions merely determine how early on in our

lives the process begins to impair our intellects and identities. 4 This is also

why, apart from a very small number of inherited, early-onset cases, almost

no one in early middle age or younger gets Alzheimer's . . . and why the

prevalence of the disease doubles every five years beyond age sixty-five, so

that victims pile up with age like the grains of rice on the Emperor's chess

board in the old fable. Our brains are slowly being enmeshed in beta-

amyloid plaques—it's just a matter of when we reach the threshold beyond

which our brains can't keep up sufficient function to carry on the lives and

identities that we have spent so many years creating. Barring some radical

new therapy, each and every one of us will be struck down by Alzheimer's

dementia if something else doesn't kill us first.

"o Captive, Bound and Double-Ironed . . ."

Beta-amyloid also causes brain damage and death in many people who

never develop Alzheimer's disease. This is because, in addition to building


up in the neurons of the brain, beta-amyloid also clings to the interior sur

faces of its blood vessels. The resulting condition, called cerebral amyloid

angiopathy (CAA), is a crusting-up of these pipelines of oxygen and nutri

ents, weakening them and reducing their ability to flex in response to the

surging flow of the pulse. This leaves them vulnerable to bursting open in a

bleeding stroke.

CAA is certainly more common in people with Alzheimer's (about a

quarter of all patients have it as a complication), but as we age it becomes

an increasingly serious issue in people not struck by the latter disease. Just

5 percent of us have CAA in our seventies, but after the age of ninety over

half of us are suffering from the disease, and it is responsible for about 15

percent of all bleeding strokes in people over the age of sixty.

But there's more: beta-amyloid is just one mangled protein among

many. Less well known, and less recognized as causes of death and disabil

ity, are a variety of other age-related amyloidoses that also don't seem to be

related to an inherently malformed protein, but to the healthy version being

damaged in the rough-and-tumble of its biochemical environment. Senile

cardiac amyloidosis is one example. As you might guess, this disorder is

most clearly characterized by amyloid fibrils building up in the heart, al

though it damages the lung, liver, and kidneys, too. This buildup interferes

with the regular beating of the heart, and can cause heart failure. The fibrils

are made up of transthyretin—the rickshaw driver for thyroid hormones

that I mentioned earlier on—and while it can arise from a mutated version

of the protein, it can also result (at a slower rate) from damage to the form

that most of us carry.

As the name implies, senile cardiac amyloidosis is a strongly age-related

disease—first showing up in people over the age of seventy, and found at

pathological levels in about a quarter of people over ninety. As in the case

of Alzheimer's disease, if we all lived long enough without something else

killing us first, each of us would wind up with the lives squeezed from our

hearts by this form of aging damage. The disease is known to be a common

contributing cause of death in the "oldest old," such that about half of

people over ninety years old have diagnosable senile cardiac amyloidosis at

autopsy.

Much earlier on in life, nearly everyone gets some degree of amyloido

sis of the aorta, the main blood vessel leading out of the heart. Two differ

ent proteins are involved, one of which builds up in the innermost layer of

the aorta in an astounding 97 percent of people over the age of fifty, while

the other accumulates deeper into the middle of the vessel wall in about a


third of these cases. This amyloidosis is not currently recognized as a cause

of specific pathology or death, but again it seems that this is only a matter

of stepping over a fatal threshold that we don't reach in a normal lifespan

today because we die of other things first.

Add them all up, and amyloid deposits of any of several misfolded pro

teins in the heart are significant contributors to death in the elderly, causing

abnormal heartbeat, weakening of the muscle of the heart, "blackouts" of

the electrical activity that keeps it beating, and heart failure.

And those are just deposits of the cardiovascular system. Every one of

us becomes riddled with microscopic amyloid deposits across multiple tis

sues in the body by the time we hit our eighties. Its toll isn't widely appre

ciated because the very old are autopsied so rarely, and you just can't see

the deposits without opening a body up. This lack of curiosity about death

in the very old of today is just another example of our routine acceptance of

the massive toll of aging processes in people who have enjoyed only—yes,

only—a few score years of life.

Moreover, while the evidence is still preliminary, amyloidosis of one or

gan system or another appears to become an increasingly critical factor in

the snuffing-out of people at the extremes of the current "natural" longevity

range. Some of this evidence comes from Japan, where the presence of a

few centenarian "hotspots" has made it an exception to the widespread

pattern of voluntary ignorance about what kills the oldest old. An autopsy

study carried out at Aichi Medical Center in Japan from 1989 to 1995

found brain-wide CAA in 16 of their 19 centenarian patients. 5 Unfortu

nately, this study was restricted to the central nervous system, so it did not

provide any information on what other amyloid diseases might have rid

dled these long-lived humans' bodies or to what extent such diseases may

have contributed to their deaths. 6

Even more suggestive is the early evidence coming out of the important

effort by the newly launched Supercentenarian Research Foundation (SRF) 7

to autopsy as many "supercentenarians" (the extremely rare people who

live beyond the age of 110) as can be identified and convinced to donate

their remains to science after their deaths. Of the six who have thus far

been examined, four were felled by some form of amyloid disease (the other

two deaths were cancer victims). 8

Again, we don't yet know what the pathological consequences of many

of these deposits may be, but it seems awfully likely that they are doing us

harm—so by the engineer's definition, they're aging damage, since they're

not found in the young. Hence, you can bet your life that I want to clean


them up along with the ones that have already been exposed as culprits in

specific age-related diseases.

Alzheimer's, Amyloids, Aging

In a perverse way, then, the fact that Alzheimer's is such a widespread and

obviously terrible disease has aided the cause of general anti-aging biomed-

icine. The attention to this specific age-related curse—together with the

widespread professional and public belief that amyloid beta deposits are a

major factor in its development and progression—has driven scientists to

attack this particular form of amyloid as a therapeutic target in its own

right, and that work has opened up the strong possibility that a similar

strategy can form the basis of foreseeable therapies for amyloid-type extra

cellular damage generally. As with other cases that we've discussed in pre

vious chapters, the existence of a recognized disease that is caused by aging

damage has "legitimized" research into ways to clean it up—and, as this re

search bears fruits in new cures for these diseases, anti-aging biotech will

be able to hitch a ride to develop treatments for aging damage itself.

Alzheimer's is an especially good example of this phenomenon, be

cause it is both so utterly fearsome and so common in our parents and

grandparents (in contrast to rare and rapidly fatal disorders like the mito-

chondriopathies or the lysosomal storage diseases). As the sheer number of

Alzheimer's victims explodes as the population's biological age creeps up

ward, victims' families and loved ones have organized politically. There are

now thousands of people in the United States and elsewhere who are de

manding—and getting—enormous government investments of intellectual

and financial capital into the quest for a cure. (Indeed, for better and for

worse, Alzheimer's research now consumes over half of the National Insti

tute on Aging's budget.)

Once the view that beta-amyloid was the key to the disease became

dominant, Alzheimer's specialists (possibly because they were not

biogerontologists?) began thinking about this particular form of extracellu

lar junk along the same damage-reversal lines that underlie the engineering

approach to age-related damage generally. All that currently available treat

ments for Alzheimer's disease can do is improve the symptoms of the disease:

sadly, no existing therapy has the power to check the ongoing degeneration

of the brain itself (see sidebar, "Alzheimer's treatment today"). This does

mean that users of these drugs are better off at any given point than they


would be without them, but the underlying progression of the disease con

tinues unabated with every passing day. Functionally, even modern

Alzheimer's drugs perform the way ibuprofen and antidepressant medica

tions do for diabetics—in providing merely superficial relief from the nerve

pain that often accompanies the disease. While the pain may indeed dimin

ish, diabetics' nerves themselves continue to be savaged by the "carameliza-

tion" chemistry of that disease. (See Chapter 9 for SENS's main answer to

late-onset diabetes.)

A L Z H E I M E R ' S T R E A T M E N T TODAY

Currently, the most widely used treatments for Alzheimer's dis

ease are the cholinesterase inhibitor drugs, such as donepezil

(Aricept), rivastigmine (Exelon), and the herb galantamine

(Reminyl/Razadyne), which attempt to bolster brain functioning

by boosting levels of some of the signalling molecules involved in

some of the flagging aspects of memory. Of course, such a treat

ment is purely palliative, with no effect on the underlying disease

process. A recent study9 suggests that these drugs are even less ef

fective than is implied by their inability to prevent the brain-

ravaging effects of the disease: It appears that while the drugs

boost scores on standardized tests of some aspects of brain func

tion, they have no effects on the kind of real-world functionality

whose loss forces families to institutionalize victims.

There was hope, for a while, that a more recently introduced

drug called memantine (Namenda) would at least slow down

the progress of Alzheimer's disease, by shielding neurons against

the damaging effects of another signalling molecule (glutamate)

that can kill brain cells when present in excess. A recent trial1 0 sug

gests that this isn't so. The study compared people who had al

ready been on memantine in a six-month placebo-controlled

trial, and who were then allowed to continue taking it for an addi

tional six months, to people in the same trial who had originally

been taking the placebo but who were given the real deal for

those subsequent six months. If memantine were really slowing

down the underlying disease process, you'd expect that people

who started on the drug earlier would have been in better shape

C U T T I N G F R E E O F T H E C E L L U L A R S P I D E R W E B S 1 4 3

than those who'd had to wait through the first six months on the

sugar pills, because they would not have been suffering the full ef

fects of brain degeneration for the first six months and thus would

have more intact brains later on. But instead, it was found that the

patients who started taking the drug later quickly caught up, in

terms of their improvement over their baseline condition, with

those who had been getting it all along. This suggests that me-

mantine's effects are only on the immediate symptoms of the dis

ease.

That's good news, in a sense, for those who start taking me

mantine at a more advanced disease state, because it means

that they haven't lost anything by waiting to get started. However,

the bad news is that no one taking memantine can expect that it

will actually stop their minds slowly dying from the tangled mess in

their brains.

It's actually not clear that blocking glutamate's effects on neu

rons would be an entirely good thing in any case. As with so many

things in the finely tuned network of metabolic pathways, gluta-

mate is a molecule with two faces. While it can stimulate brain cells

to death when it's present in excess, it's also a key chemical sig

nalling molecule in the brain, required for the normal storage and

retrieval of memories. This suggests the possibility that memantine

may cause problems in the laying down of new memories, even as

it preserves the brain cells that store the old ones. There is no direct

evidence of such an effect yet, but it still isn't clear that the drug

helps much, either: While this trial did seem to show a benefit from

memantine, there were no statistically significant benefits com

pared to sugar pills in the two other major trials of the drug.

In any case, even a drug that could slow down the rate at

which brain cells are lost would be unable to prevent— let alone

reverse—the degeneration of the brain, since the underlying

damage that has already occurred is left unrepaired.

As the evidence supporting a central role for beta-amyloid in the develop

ment and pathology of Alzheimer's built up, a new hope emerged. Scientists

began talking seriously about the idea that, by making beta-amyloid itself

the target for new medical interventions, they would be able to develop new


treatments that would treat the disease instead of merely providing crutches

to a crippled—and rapidly deteriorating—mind. Once researchers had the

tools they needed, in the form of engineered mice whose brains produced

variations on human beta-amyloid that led to the formation of brain plaques

and dysfunctions of brain and memory, they could start work on testing

therapies that would target beta-amyloid directly.

New Targets, Old Rifles

But simply believing that that beta-amyloid is the main villain in the

Alzheimer's story doesn't tell you what to do about it. Thus, it's no surprise

that academic labs and pharmaceutical companies around the world have

been working on quite a variety of anti-amyloid strategies, each hoping to

make a Nobel-quality breakthrough or market a blockbuster new drug

with a desperate—and ominously, inexorably expanding—"target market."

Predictably, however, when scientists began thinking about how to

tackle the beta-amyloid plaque problem, many of them first turned to clas

sically preventative strategies typical of the old-style gerontological ap

proach to aging. Recall that beta-amyloid, like other amyloid proteins, is

formed from an essentially healthy protein—amyloid precursor protein

(APP). That protein is found in long strands woven through brain cell

membranes, and while its exact function is unknown, it's at least harmless

as long as it remains intact and in place. But occasionally, the beta-secretase

enzyme mistakenly latches onto the APP protein and chops it at an unin

tended place; gamma-secretase innocently follows suit, not recognising the

fatal flaw in the misprocessed APP; and beta-amyloid—with its exposed,

sticky binding sites—is released to wreak its havoc in the brain.

With this in mind, one of the first ideas for an anti-amyloid therapy was

to create drugs that would dampen down the activity of these enzymes,

thereby cutting down the production of beta-amyloid. This in turn would

reduce plaque formation, and thus either slow down or prevent the emer

gence of the disease.

First out of the gate was a drug that interfered with gamma-secretase ac

tivity. Animal studies showed that even a single dose of the drug could reduce

levels of soluble, pre-plaque beta-amyloid in both the brain and the plasma,

and it was duly moved through the development pipeline into the "Phase II"

trials that are designed to give preliminary evidence of a drug's efficacy and

safety in a moderate-sized population of people with the disease.


That was in 2001. I'm writing this in early 2007, and to date there has

been total silence about the results of the trials of this first gamma-secretase

inhibitor. We may never know what happened, but we may be able to

guess. Even as the drug was being tried in humans, greater understanding

of the role of gamma-secretase in the body emerged. A question that had

long hung over the enzyme-inhibition approach was what, exactly, the en

zyme was supposed to be doing in the body.

Many harmful mutations lurk in isolated pockets of the human family,

but we all have gamma-secretase in our brains—and, as I discussed in Chap

ter 3, evolution does not design us to suffer horrible diseases. Although

gamma-secretase has the unfortunate long-term side effect of beta-amyloid

production, scientists always had in the back of their minds the acknowl

edgement that it had to serve some useful purpose, too. And, sure enough,

researchers discovered while the trial was still progressing that gamma-

secretase operates on several proteins in the body—including Notch receptor

1 (NOTCH1), a protein with critical functions. By this I mean really critical:

They include the activation of stem cells that renew damaged muscle tissue,

the growth of new blood vessels, and the maturation of some kinds of im

mune cells.

So, what happens to these important biological processes, when you

start interfering with an enzyme that's needed to keep them going? Animal

models, using either a "knockout" of the gamma-secretase gene or an alter

native gamma-secretase inhibitor drug, showed that dampening down the

enzyme clearly prevented immune cells from developing in both the bone

and the thymus, reducing the number of these cells and causing pathology

in the gut. It seems highly plausible that the reason for the stony silence on

the human trials is a similar profile of side effects.

However, some researchers are still chasing after therapies based on

the same basic strategy. In 2002, researchers at Eli Lilly presented animal

data showing that LY450139, the code name for a new gamma-secretase in

hibitor, lowered beta-amyloid levels in Alzheimer's mice without interfer

ing with NOTCH1. As this chapter was being drafted in 2006, the results

of an early human trial in seventy Alzheimer's patients came in, showing

that the drug reduced levels of beta-amyloid by 38 percent without appar

ently causing any serious side effects. By April 2006, the company had part

nered with several universities and hospitals and was gearing up to perform

a larger clinical trial to see if it could actually affect the disease. Elan Phar

maceuticals is also continuing to research a gamma-secretase inhibitor.

But deactivating NOTCH1 is far from the only potential concern with


these drugs. Remember, gamma-secretase is also an essential partner in the

normal, non-amyloidogenic metabolism of APP into products that appear

to be essential to the functioning of neurons. It's unlikely that you can get

away with ratcheting its normal activity down by force with no negative im

pact on the very brain function that researchers are desperately trying to

preserve. It may just take longer than the brief six weeks over which the

new drug's first safety test was performed. The new trials are just starting to

recruit patients at this writing; we'll see how they fare in the clinic, and

keep our fingers crossed for the people taking them.

Other scientists are pursuing a slightly different version of the same ba

sic strategy. Some are developing drugs that inhibit beta-secretase, or that

turn up the activity of alpha-secretase, with whose normal processing of

APP beta-secretase interferes. Because such drugs are still in the early stages

of development, we don't yet know what their side effects will be, but again

it seems unlikely that the activity of an enzyme produced normally through

out the body—and especially in the brain—can be altered without cost. For

instance, one specter that already looms over the beta-secretase inhibitors

(based on animal studies) is that they may make users more vulnerable to

some psychological disorders. While very young animals with their beta-

secretase genes knocked out seem to be physiologically more or less normal,

they are timid and don't like to explore their environment, and seem to run

through serotonin (the chemical messenger whose metabolism is modulated

by drugs like Prozac) abnormally quickly.

Freeing the P r i s o n e r s . . . or Letting Loose the Inmates?

Other scientists are pursuing an alternative approach that is, superficially,

more in line with the engineering principles that I have advocated.

Namely: to ignore the formation of beta-amyloid itself, and instead focus

in on the process whereby beta-amyloid becomes aggregated into neuron-

enmeshing plaques. A surprisingly large number of drugs and even herbal

concentrates—from extracts of the spice turmeric (used in curries) to cus

tom drugs with the highly marketable moniker beta-breakers—either inter

fere with the glomming-together of beta-amyloid into plaque fibrils, or

even break existing aggregates a p a r t . . . in a test tube. Most of these com

pounds never worked out once they got beyond the petri dish and into a liv

ing, breathing organism, but a few have been shown to reduce the plaque

burden in animals genetically engineered to produce large amounts of


beta-amyloid, and a few of those are now going into clinical trials in people

with Alzheimer's disease.

Here, however, we once again run into the problem of over-reliance on

our hypotheses about what biochemical processes "cause" the disease. In the

other amyloidoses, the connection between fibril and pathology is pretty ob

vious. Indeed, you can dramatically extend life expectancy in patients with

several kinds of amyloidosis by "simply" replacing the amyloid-strangled or

gan with a transplanted one free of fibrils.

But the reality is that, despite a decade of intense research into the

"amyloid hypothesis" of Alzheimer's disease, we still don't understand the

mysterious metabolic underpinnings of the disease. Even among the major

ity of researchers who are convinced that beta-amyloid is the key to

Alzheimer's, the consensus around the detailed mechanistic role of the pro

tein in the disease is as shallow as it is wide. Controversy continues to rage

about what exactly links it—the protein itself, and/or the plaques that form

from it—to the decay of brain and body that we see in its victims. Thus, the

premise that beta-amyloid plaques cause Alzheimer's—or link the underly

ing metabolic defect(s) to disease—is still not enough in itself to tell you

what should be done about them.

If anything, the balance of evidence is that it may not be the plaques

themselves that impair neurological functioning the most, but the soluble

beta-amyloid oligomers: short chains, made up of just a few single beta-

amyloid molecules ("monomers") linked together in the same way that

plaque fibrils are, but whose small size allows them to remain dissolved in

the fluid bathing the cells of the brain rather than precipitating out into de

posits. In cultured cells and in experimental animals, beta-amyloid oligomers

derived from human nerve cells clearly disrupt neuronal function and in

terfere with normal memory, in ways that are not observed with either the

beta-amyloid plaques that they form or the lone "links" of beta-amyloid

monomers of which they are composed. After being microinjected with

human-derived oligomers, rats become confused and forgetful. Beta-

amyloid monomers don't have the same effect, and while giving animals or

brain cell cultures chemicals that clear all forms of beta-amyloid (oligomers

and monomers) out of the fluid bathing the neurons prevents the negative

effects of exposure to a mixture of oligomers and monomers, an enzyme

that selectively degrades free beta-amyloid monomers while leaving the

oligomers intact provides no protection.

Likewise, the rats' memory function is largely recovered a day after in

troduction of the oligomers, when they have been cleared out by the animals'


natural protective systems. This again suggests that the oligomers, rather

than the plaques that they form, are the guilty parties in cognitive function.

And indeed, preliminary studies suggest that the oligomers act as the mo

lecular equivalent of dust in the eyes of neurons, interfering with their abil

ity to receive signals from other neurons and pass the signal on to their

internal machinery. Adding to the uncertainty, one group have reported a

mouse model in which abundant plaques form but no neurological deficits

result.

Another series of experiments strongly suggests that the plaques are

the result, rather than the cause, of the widespread death of neurons in the

Alzheimer's brain. 1 1 This study looked in detail at the location of both sol

uble amyloid species and plaques in the brains of people who had died of

the disease. Soluble amyloid was found accumulated in still-intact cells

within their lysosomes (the cellular garbage disposal units discussed exten

sively in the last chapter). Areas with very high levels of amyloid showed ev

idence of the rupturing of neurons, with beta-amyloid and the lysosomes'

digestive enzymes dispersed outward from a central locus in a pattern that

suggests nothing so much as a bomb blast. And wherever plaques were

found, the researchers also found the remnants of a destroyed neuron's cell

nucleus in the debris.

The strong suggestion was that the cells had been trying to dispose of

the toxic amyloid oligomers by dumping them into the lysosome. Remem

ber, again from the last chapter, that the Alzheimer's brain shows clear evi

dence of dysfunction of these organelles. Moreover, a lot of the beta-amyloid

found inside brain cells is actually clustered in and around lysosomes, and

the aggregates themselves are in fact naturally taken up and degraded in mi

croglia (the immune cells of the brain), but at a rate that is too slow to keep

up with plaque formation.1 2

This suggests that the burden of amyloid may eventually overcome the

capacity of lysosomes to dispose of it, leading to the death-spiral of dys

function outlined previously—and eventually to the death and rupture of

the cell, during which the beta-amyloid and lysosomal enzymes spew forth

from the dying neuron, creating plaque deposits like so much slag from a

bombed-out building.

However, the innocence of plaques in Alzheimer's disease can't be as

serted any more confidently than their guilt. The beta-breakers that have

been shown to be effective in animal models (as opposed to just test tubes)

do restore memory function as they break up the plaques. And again, a

mere glance at the snarling webs of amyloid-enmeshed cells of the


Alzheimer's brain defies the observer to accept the notion that the plaques

are harmless.

One theory that may reconcile these conflicting conclusions is the idea

that, at least in the short term, the plaques' most damaging effect on the

brain is to act as reservoirs for the beta-amyloid oligomers. You may have

done simple experiments involving solutions in junior high-school science

class, in which a substance is dissolved at very high concentrations in a glass

of water. Eventually, levels reach so high a concentration that the water

can't hold any more, and a crystal precipitates out of the solution.

But the teacher may have explained to you—or even demonstrated—

that the crystal is not a static entity, but exists in a state of "dynamic equi

librium," with some dissolved material continually precipitating out onto

its surface to build it up even as some of its existing surface molecules are

continually dissolving out into solution. The volume of crystal will remain

constant at a given solution concentration, as the rate of dissolution out of

the crystal remains equal to the rate of precipitation into it. But of course, if

you add more water or dissolved material into the solution, the equilibrium

shifts accordingly.

The same thing, more or less, may be happening with amyloid plaques.

As the concentration of beta-amyloid monomers and oligomers increases,

they aggregate into plaques, which keeps the level of dissolved oligomers

lower than it might otherwise be, thus effectively reducing their potential

toxicity to local neurons. But when the level of oligomers dissolved into the

fluid is reduced, the aggregated oligomers dissolve back into solution,

maintaining their signal-jamming influence in a toxic steady state.

This potentially creates a real dilemma for therapies designed to deal

with beta-amyloid. Using drugs like beta-breakers to prevent amyloid fib

rils from forming, or to break existing plaques apart, would free up beta-

amyloid oligomers that would otherwise have been sequestered in the

plaque mass—which would actually expose neurons to more oligomeric in

terference than just leaving the plaques alone or even letting them build up.

In fact, both things would happen at once—and this could well have

parallels in the Alzheimer's brain. It seems very likely to me that beta-

amyloid plaques play—or eventually would play—a similar role in the

brain of the Alzheimer's patient to what, say, transthyretin deposits do in

the hearts of people struck by senile cardiac amyloidosis: you can't look at

the mess of a victim's brain and not suspect that the plaques have been

choking neurons to death. While the evidence is strong that any inter

vention which results in an increase in neuronal exposure to soluble


oligomers of beta-amyloid can be expected to damage the brain, simply

leaving the plaques to grow larger and larger as the diseased neurons con

tinue to produce beta-amyloid (and/or to rupture and spill unprocessed

beta-amyloid out of their lysosomes) surely sets the brain up for an even

greater problem further down the road.

These intriguing theoretical questions are the kind that excites the cu

rious minds of scientists; moreover, answering those questions seems to

many such scientists to be the natural way of identifying and developing

treatment for this terrible disease. As for other kinds of aging damage, how

ever, I believe that this assumption is flawed. Let me say it again: We do not

need to understand in detail how aging damage accumulates, or by what

mechanism it wreaks its havoc, in order to undo that damage. However ex

citing an intellectual challenge it may be to sort out the exact pathway that

leads from the fatal nips and tucks on APP, to beta-amyloid formation, to

plaques, lysosomal dysfunction, cognitive impairment, and neuronal cell

death, the bottom line in terms of the biomedical challenge is that we have

here a material that is clearly accumulating and altering the composition of

our aging and diseased bodies. When I see that, I say: it must go.

You can probably guess, by now, what sort of anti-amyloid therapy I

prefer. While the remaining concerns about the exact role of plaques and

oligomers in the disease process make simply breaking apart the aggregated

beta-amyloid a potentially risky strategy, that doesn't rule out a solution

based on removing the plaques in whole cloth. That would eliminate the

source of the problem, no matter what step in the formation, metabolism,

or aggregation of the constituent material is in fact the key to its toxicity.

Such an intervention would be classic anti-aging engineering as I've envis

aged it—if it could be done.

Fortunately, we should know very soon. A potential solution is already

undergoing clinical trials.

" Immune" from Plaque: The Beta-amyloid Vaccine

As I mentioned earlier, researchers found evidence some time ago that mi

croglial cells—the immune cells of the brain—slowly eat up and digest away

beta-amyloid deposits from nerve cells. Unfortunately, it was clear that the

rate of clearance was not nearly high enough to keep up with the pace of

deposition in Alzheimer's patients. But researchers guessed that this natu

ral defense mechanism could be stimulated to greater throughput. The ob-


vious way to do this would be as we do for other targets of the immune sys

tem: with a vaccine.

The vision: inject patients with beta-amyloid, and the silent sentinels of

the immune system would be roused up in defense, seeing the protein as a

foreign invader. The same forces that your body marshals against chicken

pox or influenza would be mobilized for an all-out war on the brain-

choking protein, churning out antibodies specific to it and inducing the

brain's microglial cells to go on a search-and-destroy mission against brain

beta-amyloid.

This was an even more exciting idea than it might at first appear, be

cause an anti-beta-amyloid vaccine would be expected to have an even

greater impact against Alzheimer's disease than had the vaccines used

against earlier epidemics. Such vaccines had allowed us nearly to wipe out

diphtheria, polio, and measles in developed countries by preventing new

cases from emerging. The promise of a vaccine targeting beta-amyloid was

that it would actually cure all but the most advanced cases of the disease.

Armies of activated microglia, their appetites for beta-amyloid whetted,

would actually consume and thereby remove the existing beta-amyloid de

posits. Once those choking fibrils were removed, the brain's normal

structure—and thus, function—would be restored. 1 3

Critically, this approach should work no matter what theory of the link be

tween beta-amyloid and memory loss turned out to be correct. (It would not be

the whole solution if other hallmarks of Alzheimer's, such as the intracellular

neurofibrillary tangles, were also contributing to disease progression—but

SENS incorporates solutions to those other aspects too, as you've seen.) The

vaccine cleared out the plaques—and also, it shortly turned out, the more solu

ble oligomers, even inside the nerve cell itself14—not by breaking them apart

into their constituent elements, but by causing immune cells to internalize and

digest them.1 5 Because no soluble beta-amyloid is released by such an ap

proach, there is no risk of doing new damage as levels of the soluble form rise:

beta-amyloid just goes away, clearing neurons of its malign influence no matter

what its exact mode of toxicity might be.

It turned out to be a relatively easy matter to test this concept in ani

mals engineered to develop a version of Alzheimer's disease. While vac

cines against viruses must be carefully modified to ensure that they are

close enough to the real thing to set off the immune system's alarms, but yet

different enough that they don't actually infect people with the disease, no

grand feat of molecular engineering was used in the first test of the concept:

mice were simply injected with aggregated human beta-amyloid.


It worked smashingly well from the outset. Plaques quickly regressed

from the mice's brains. The swelling and dysfunction of the neurites

(the branches that transport chemical messengers from one nerve cell to

the next) faded away, leaving healthy, functional units. The dense, inflam

matory overgrowth of supporting cells around the neurons retreated. 1 6

And memory function—evidenced by the animals' abilities to find hidden

platforms in flooded mazes—became more like that of younger, healthy

animals . 1 7 , 1 8

The company coordinating this work, Elan Pharmaceuticals, obtained

results in many different models of engineered mice, each with a different

mutation in the processing of APP. Best of all, the treatment appeared to be

quite safe. Contrary to what had been feared, the immune attack on the

beta-amyloid around the animals' brain cells did not cause collateral dam

age to the fine network of supporting cells onto which the plaques were

glued. Likewise, some had feared that the immune attack on beta-amyloid

would be so aggressive that it would punch holes in the protective shield

that protects the brain from the toxins in the bloodstream, triggering a

flood of foreign substances into the brain from the rest of the body; but lit

tle evidence of such an effect was found. The FDA was so impressed with

the results that it quickly gave Elan the nod to move their vaccine—code-

named AN-1792—into placebo-controlled clinical trials.

Nearly 400 patient volunteers were recruited, of whom 300 received

the amyloid vaccine and 72 were given injections of saline solution as a

placebo control. Their baseline condition was determined, their mental

state and functionality were assessed on a battery of neuropsychiatric and

clinical tests, and a regimen of periodic injections was instituted.

Twelve months later, disaster struck.

A Fire in the Brain

Just a few months after this trial had begun, some patients started exhibit

ing serious side effects. Of more than 300 patients recruited from 28 clini

cal centers across Europe and North America, about one in 15 developed

meningoencephalitis, a life-threatening swelling of the brain, apparently as a

result of an overreaction of the immune system inside the brain itself.19

As soon as the side effect was discovered, the trial was halted, sending

researchers scrambling to try to figure out what had gone wrong. The prob

lem came as a complete shock. The vaccine had been tested in mice with a


wide range of genetic abnormalities, each leading to Alzheimer's-like

plaque formation from a different defect in the synthesis or metabolism of

APP, and no such side effect had been observed—this despite the fact that

scientists had been much more aggressive in their treatment protocols with

mice than they would dare to be with human patients.

How such a crisis could occur, after such careful preclinical testing, has

been documented extensively in the media and the academic literature, and

I think it's too much of a digression to describe here. The important point is

that researchers rapidly homed in on the problems with the first vaccine—

and, as we shall see, on how those problems can be overcome.

Snatching the Ore from the Smelter 's Ashes

The first trial proved catastrophic for some patients, and it was terminated

before science could assess the full range of effects of the vaccine—

positive and negative. But despite—and in a way, because of—the con

straints imposed by this serious adverse reaction, researchers were

desperate to squeeze every available bit of data that they could from the

trial, to make up for its human and financial cos ts . 2 0 , 2 1 , 2 2 Through careful

sifting of the data, scientists managed to collect some preliminary informa

tion suggesting that, despite the horrors of inflamed brains in a few pa

tients, immunization with beta-amyloid fundamentally does work as a

therapy in humans. And when combined with further animal studies, the

findings also suggested ways to avoid this side effect (and others) in future

vaccines—some of which are either under development, or even in clinical

trials, already.

In the immediate aftermath of the study's sudden termination, infor

mation about the patients was still scattered throughout the twenty-eight

independent clinical centers at which the patients had received treatment.

Preliminary assessments of the readily available information were not

promising: researchers saw little evidence of improvement in the memory

or other cognitive functions of people in the trial. But as the dust settled

and researchers began to collect and analyze volunteers' full medical rec

ords, a new pattern emerged. 2 3 A given vaccine (any vaccine) does not do

the same to all its recipients: some people create a stronger immune re

sponse to it than others. By separating out those participants whose blood

work showed that they had mounted a substantial antibody response to

the injected beta-amyloid by the time the study was shut down (fifty-nine


volunteers) from the rest (who had not), scientists were able to show that

those who had responded well to the vaccine had, apparently, fared better.

This finding took time to emerge because it was initially obscured by

the statistics. When the researchers looked individually at each of the cog

nitive tests that volunteers had been administered, they could find no dif

ferences that passed the test of statistical significance. However, an

integrated analysis of the whole battery of tests suggested that people

whose immune systems had responded to the challenge suffered less de

cline during the study period than had people administered the placebo—

a difference that was only beginning to become clear at the twelve-month

mark when the trial was halted. Of particular interest was the fact that the

emerging difference was most apparent for a composite score on the mem

ory tests. And most suggestively, there did seem to be a sort of "dose-

response" effect, with the greatest improvements in scores on overall

memory, immediate and delayed memory, a nine-component memory

score, and possibly a test of "executive function" (that is, higher-order

brain functions involved in governing ourselves in a goal-directed fashion

in the beginning and over time) in those whose antibody responses were

strongest.

These results were all the more impressive considering the likelihood

that most of the active responders were suffering from low-level brain in

flammation and "ministrokes" triggered by the vaccine—a possibility sug

gested not only by autopsy findings and animal studies, but by the fact that

headaches and confusion were reported as side effects so much more often

in subjects who had received vaccination than in those who had received

the placebo. Indeed, studies in breeds of Alzheimer's mice that had beta-

amyloid deposits on their vasculature, and were thus vulnerable to micro-

hemorrhages in response to the vaccine, still showed some cognitive

improvements, despite the direct damage their brains suffered from the

tiny bleeds. If your brain function is being preserved in spite of a quiet,

chronic attack on it by your own immune system, the implication is that

something else about your underlying clinical condition has improved even

more. A vaccine that would clear out beta-amyloid (as this one appears to

do) without causing the inflammatory side effects would therefore be ex

pected to yield a much more robust improvement in the workings of the

mind.

Another interesting finding came when researchers looked at the levels

of the protein tau, which is the major constituent of neurofibrillary tangles,

in the fluids bathing the central nervous system (the cerebrospinal fluid, or


CSF). Even though they only had about ten subjects in each group with

good enough data to compare, the medical teams did observe that the vac

cine responders had lower levels of tau than did the patients receiving

placebo. While it's very indirect, this might be a sign of reduced rates of

brain cell death, since high levels of tau in these fluids are associated with

the death of neurons in people with the disease.

What about evidence on the intended effects of the vaccine—its ability

to actually clear out beta-amyloid plaques? Unfortunately, it's not yet rou

tine for scientists to look into the brain to see the plaque burden in people's

brains before they've died, although new imaging techniques to do just that

have been developed and are being tested for accuracy now. What can eas

ily be done is to analyze levels of beta-amyloid in the cerebrospinal fluid. In

animal studies, vaccination against beta-amyloid almost always results in an

increase in CSF levels of beta-amyloid—a finding usually interpreted as a

sign that the vaccine is helping the animals to clear the stuff out of their

brains and then transport it elsewhere in the body for disposal. This effect

was not seen in the small number of trial volunteers for whom scientists

had samples that they could compare. But we have another, more direct

source of evidence on the subject: the three vaccine responders who died

over the course of the trial. While one must again be cautious in reading too

much into the results observed in just three people's brains, autopsies of

these volunteers by independent groups did show a dramatic reduction in

levels of plaques in key regions of each of them as compared with control

subjects.

Moreover, pathologists examining these brains found microglia in

close proximity to many of the plaques that remained, suggesting that the

vaccine was working as scientists had always hoped: the activated immune

system had successfully mobilized microglia to clear out the deposits of

beta-amyloid. This conclusion was further bolstered by a study—only com

pleted after the end of the human trial—showing that old Caribbean green

monkeys given beta-amyloid vaccination exhibited huge (66 percent) re

ductions in beta-amyloid levels in the brain, and a complete absence of

plaques, and that the dense tangling-up of neurons' supporting glial cells

usually seen in human Alzheimer's patients was considerably reduced.24

This is an important piece of supporting evidence, because these monkeys

develop some Alzheimer's-type pathology naturally as they age, and are

much closer relatives to us than any mouse. The researchers who reported

this finding are currently working to develop ways to assess the monkeys'

cognitive function.


The Next Beta-amyloid Vaccine

All of this tantalizing, albeit inconclusive, information has once again

erected the banner of beta-amyloid vaccination as a true cure (or at least a

major component of a cure) for Alzheimer's disease. We've learned enough

about both the potential of the vaccine and the reasons for the deadly brain

inflammation to develop a variety of new approaches to the basic strategy,

one or more of which will almost certainly prove effective without putting

its recipients at risk.

The key to designing a safe vaccine is, of course, to avoid enraging the

immune cells that attacked the original subjects' brains in the first trial even

as the microglia were loyally cleaning out the amyloid plaques. There are

several ways that this might be done, and each of them now enjoys support

in animal models of the disease—supporting their efficacy while providing

evidence that they will not have a deadly immune side effect.

One relatively straightforward approach that has already entered clini

cal trials is something called passive vaccination. Unlike a conventional ac

tive vaccine, in which the patient receives the offending agent itself (in this

case, beta-amyloid) in order to signal the immune system to produce its

own antibodies in response, passive vaccination involves directly providing

the very antibodies that are desired, bringing out the immune response that

the same antibodies elicit when they are produced by the body. The advan

tage of this approach is that it would allow scientists to choose which anti

bodies would be circulating throughout a patient's body. These antibodies

might be chosen, or even custom-made, to activate the type of response

that sends the microglia out to break down and digest the amyloid de

posits 2 5 without the risk of eliciting the undesired antivasculature response.

The main disadvantage of this approach is that it would not induce the

kind of semipermanent immune vigilance we've come to expect from vacci

nation against diseases like mumps or polio, but would instead require pa

tients to receive regular reinjections of the antibodies to keep their

amyloid-fighting supplies topped up. But even this apparent inconvenience

has an upside: because the recipient's immune system isn't put into a long-

term state of vigilance against beta-amyloid, physicians can stop treatment of

an individual patient—or even stop an entire trial—at any time in case of side

effects, without the fear that the body will remain in a destabilized

autoimmune-like state of the kind elicited by the original vaccine.

Another approach is to manufacture an active vaccine composed of only

part of the beta-amyloid molecule. When scientists looked at the immune


response to active vaccination with the whole beta-amyloid molecule, they

found that a mixture of different antibodies was being produced. Only a

small number of those antibodies were of a type that harms the vasculature—

and, significantly, these antibodies were only observed in humans adminis

tered the original vaccine, and not in the mice or monkeys that received the

same vaccine and had not suffered the tragic assault on the brain. These anti

bodies were sensitized to only one segment of the total beta-amyloid protein,

located in the middle of the molecule. By contrast, in mice, monkeys, and hu

mans, most of the antibodies were of types that would mobilize the immune

system against a completely different segment of the beta-amyloid molecule,

located on its far end.

Since it's reasonably clear that the antivasculature response is not only

unnecessary (since it isn't seen in the animal models with active or passive

vaccination, yet these procedures dramatically clear out amyloid and im

prove memory) but is extremely harmful (due to its role in brain inflamma

tion), it seems highly likely that a vaccine based on the above principles will

work fine and be free of the risk of brain inflammation so long as it reacts

only to this key subsection of the protein. Such a vaccine would induce the

desired immune response on an active basis, without sending the body's

immune system on a misguided mission against the very brain in whose de

fense it was aroused.

To date, several vaccines have already been developed based on this

principle. They work by binding the key segment of the beta-amyloid pro

tein to other proteins or antigens, or by combining it with appropriate im

mune stimulants, or by joining several such segments together into a sort of

beta-amyloid molecular pincushion, all in an effort to maximize the anti

body response to the vaccine without initiating the overreaction. These

vaccines have all been shown to reduce levels of beta-amyloid, and often of

plaques—some of them using very convenient delivery systems, such as

transdermal patches similar to the ones widely used for nicotine treatment,

or else the kind of nasal spray now used for quick decongestant relief of

stuffed-up noses.

And even this has not exhausted scientific creativity. As this book was

in preparation, for instance, researchers at the University of Texas' South

western Medical Center reported that injecting animals with the DNA for

the most toxic form of the beta-amyloid proteins, smuggled under the skin

inside tiny gold microparticles, led to production of the protein and to the

body responding with a rigorous and apparently safe antibody response.

The result: after receiving eleven injections over the course of several


months, the Alzheimer's mice enjoyed a 60 to 77.5 percent reduction of

plaque burden. 2 6

As I mentioned, the most well-studied passive vaccine is already in

mid-stage clinical trials orchestrated by Elan Pharmaceuticals. And while

this vaccine was the first out of the gate, the race to develop a clinically ef

fective and safe vaccine to defeat beta-amyloid is very much on. Indeed, the

question today seems to be not so much whether vaccination against amy

loid will work, but which of these many ingenious strategies will ultimately

prove to be most effective and safe. Surveying the progress made so far, we

can say with a high degree of confidence that we should soon be able to

harness the ancient powers of the immune system to cut our way through

the mind-stealing webs of beta-amyloid, redeeming the captive minds that

they bind.

Amyloid Vaccination: Beyond Alzheimer's

I've spent so much time discussing the Alzheimer's beta-amyloid vaccine

that you may well have forgotten how I got started: by noting that beta-

amyloid is just one famous example of a class of extracellular aggregating

proteins ("amyloids") associated with aging and with age-related diseases.

And no, I'm not repeating the mistake of the National Institute on Aging in

this regard, which is to throw nearly half of all of its resources every year

into Alzheimer's research, at the expense of its real mandate, which is (or

ought to be) to find ways to treat aging itself rather than one particular age-

related disease. Instead, I've been guiding you through the vaccine's

progress simply because it is in such an advanced state of clinical develop

ment. There's every reason to think that we will be able to exploit the same

sort of immunological strategy to tackle most of the other age-related disor

ders caused by coatings of extracellular junk.

Next to beta-amyloid vaccination for Alzheimer's disease, the immuno

logical amyloid-buster in the most advanced state of development is a vac

cine for systemic Ah amyloidosis, also known as primary amyloidosis. I

briefly mentioned this form of amyloidosis early on in this chapter. This is

the most common form of amyloidosis in the United States and some other

industrialized countries—it strikes two to three thousand Americans annu

ally. It's the result of overproduction by a specific cell type, plasma cells, of

immunoglobulin light chain (L—thus "AL," for "Amyloidosis Light-

chain"), a component of a class of antibodies.


However, I'm not going to spend much time on AL amyloidosis here,

because it's not an age-related amyloidosis and the amyloid involved may

differ in important ways from ones that are age-related. The main differ

ence is that it's laid down so extremely fast that it may not have the same

degree of problematic cross-linking as age-related amyloids. The main

thing I do want to tell you about AL amyloidosis concerns an immunother

apy protocol for it that shows promising signs of being transferable to age-

related amyloidoses.

The existing therapies for AL are decidedly inadequate. Until recently,

the standard intervention was a regimen of high-dose chemotherapy de

signed to kill off the originating plasma cells, often combined with bone

marrow transplants to replace some of the other blood cells that are de

stroyed in the process. More recently, a new chemotherapeutic drug called

I-DOX has been used, after the serendipitous discovery that it could accel

erate removal of systemic AL amyloid plaques through an as-yet unknown

mechanism that apparently does not involve suppressing plasma cells. But

even this new therapy tends to cause blood disorders, and both these treat

ments are only helpful for people with soft-tissue deposits, extending no

benefit to the more serious cases involving the heart or kidneys. They're

also not terribly successful at saving lives, with a mortality rate of about 40

percent.

At the turn of the millennium, scientists in Dr. Alan Solomon's lab at

the Human Immunology and Cancer Program at the University of Ten

nessee Graduate School of Medicine developed a new animal model for

AL, created by simply injecting mice with human light-chain amyloid ex

tracted from the livers or spleens of patients who had died of the disease.

The AL quickly began forming amyloid "tumors" in the animals, the size of

which varied with the amount of material the animals were administered: at

higher doses, the amyloid masses on their backs grew so large that they

could be felt by hand. 2 7 , 2 8

As they explored the effects of the disease on the animals, Dr.

Solomon's group demonstrated that antibodies against a segment of the

unique "beta-sheet" conformation of the light-chain amyloid fibrils were

partially breaking down the deposits, making them more susceptible to im

mune attack. When they took amyloid tumors out of mice, subjected them

to such antibodies and then returned the tumors into the mice, the animals

cleared them out twice as quickly as new tumors of similar size. Clearance

was also speeded when the original, unaggregated amyloid extracts were

pretreated with antibodies before being injected. Even immune-deficient


mice cleared out the deposits more quickly when they were given antibod

ies along with the amyloid extracts. 2 9 One such antibody—an immunoglob

ulin G1 antibody that they named 11-1F4—was found to have the strongest

"homing instinct," rapidly converging on tumors composed of either of the

two major classes of human light-chain amyloid fibrils, whether in a test

tube or in mice bearing them. Just as important, the antibody was found to

target the amyloid specifically, without infiltrating tissues anywhere else in

the body or samples of human tissue. And it also worked on pre-formed AL

amyloid.

A Jack-of-All-Amyloids?

As I mentioned, the reason I'm telling you about 11-1F4 is not because of

its effects on AL amyloidosis. The one disadvantage of Solomon's model of

systemic AL amyloidosis was that it's an imprecise model of the human dis

ease, with little spread of the deposits to major organs. Noting this, his

group sought ways of testing it against other amyloid diseases, such as amy

loid protein A amyloidosis (AA—also termed "inflammatory" or "second

ary" amyloidosis), the most common amyloid disorder outside the United

States. 3 0 AA has the advantage of being easy to induce as a full-blown dis

order in many strains of mice: you simply inject them with chemicals like

silver nitrate that induce a strong inflammatory response, resulting in over

production of serum amyloid A (SAA), a protein produced by the liver dur

ing times of inflammation. Like immunoglobulin light chain, SAA is only

partially degraded by the body's macrophages, resulting in the release of

sticky, half-digested SAA fragments that tend to clump up and accumulate

in the kidney and liver. This is the genesis of the disease in both mice and

humans, so the amyloid disease that results when mice are given these in

flammatory chemicals very closely mimics its human counterpart.

Surprisingly, the University of Tennessee team found that the 11-1F4

antibody also reacted to AA amyloids from mice—and that it cleared them

out of affected mice . 3 1 , 3 2 In fact, it was very nearly as effective against AA

deposits as it was against the original AL target, with the average organ

amyloid burden dropping by over three-quarters in liver and spleen alike!

This may be because the molecular architecture underlying the different

fibrils' stickiness is similar, leading to a similar antigenic profile. It may also

be related to the long-established fact that extracts of AL amyloid deposits

accelerate the development of AA in response to inflammation in mice. If


so, maybe the aggregating properties of the different amyloids are such that

they can interact, with one serving as a sort of crystallizing center around

which other amyloids gather. Think of a small deposit of cooked-on food

on the surface of a pot. If the stain isn't immediately scrubbed out, it be

comes increasingly stubbornly imbedded on its surface by future cooking,

and then begins to catch food particles from subsequent meals, slowly ex

panding into a larger and larger stain that is ever more difficult to remove.

Even more remarkably, the University of Tennessee team then went on

to show that 11-1F4 could also react with, and remove, amyloids based on

transthyretin (TTR), the thyroid-hormone transporting protein whose ag

gregation causes senile cardiac amyloidosis, and which is a cause of death

in so many of the oldest humans among us today. If passive immunization

with 11-1F4 can reverse the course of both of these major forms of amyloi

dosis, we are well on our way to clearing out some of the most important

sources of extracellular junk in the population at large—as well, potentially,

as other forms of amyloidosis that are less common causes of death only be

cause our lives are currently so brief.

This is exciting research, and the next step for the antibody is clearly to

test it out in humans with the corresponding amyloidoses. For this to be

done, the antibody must first be "humanized." Remember, while the light-

chain amyloids that the antibodies remove are derived from humans, the

agent that's doing the removal is a mouse antibody, which would probably

not interact well or safely with the human immune system. To overcome

this problem, Dr. Solomon's team "chimerized" the antibody, combining

its antigen-seeking "business end" with a human "handle." The resulting

antibody still recognized both light-chain amyloid and amyloid protein A

aggregates, and even cleared them out of mice just as the original vaccine

had done. The results are so promising that the National Cancer Institute's

Drug Development Group has arranged for large-scale pharmaceutical pro

duction of the new antibody, with the intention of moving it into prelimi

nary human clinical trials.

Open Possibilities

There is every reason to believe that this kind of immune-based, vaccina

tion approach to amyloids, demonstrated in animal models of Alzheimer's

disease and three human amyloidoses (and now in clinical trials for the for

mer), will also work in other cases of cellular bindweed. Take, for example,


amylin, or "islet amyloid polypeptide," whose amyloid-inducing properties

I briefly mentioned early on in this chapter. Amylin aggregates accumulate

on insulin-producing beta cells in the pancreases of nearly all people with

type 2 (late-onset, non-insulin-dependent) diabetes. Either the aggregates

or the soluble oligomers of which they're composed appear to play some

role in the gradual dying-off of beta cells that occurs as the disease pro

gresses, 3 3 leading to the failure of the body to produce enough insulin to

keep up with the incessant surges of sugar that accompany every meal.

No one has yet tried to develop a vaccine to remove these deposits, but

the feasibility of such an approach is suggested by the fact that amylin fib

rils have been identified inside macrophages harvested from areas adjacent

to the amylin deposits, where amylin accumulates without being fully de

graded. Moreover, amylin fibrils are engulfed by and accumulate within

macrophages exposed to them under test-tube conditions. 3 4 All of this sug

gests that that the immune system mounts an attack against this form of ex

tracellular junk just as it does against amyloid beta and the junk responsible

for secondary amyloidosis—in which case, there is every reason to think

that this attack could be strengthened with a vaccine similar to those cur

rently in the pipeline for those other amyloidoses. The therapeutic promise

of such an approach would be even greater if it were combined with a

souping-up of the macrophages' lysosomes with enzymes that are more

able to digest the amylin fibrils—-a job that cries out for the use of the

LysoSENS approach that I discussed in the last chapter.

Other forms of amyloidosis could also fall before an infusion of tar

geted antibodies or other vaccines. And while the focus for drug develop

ment today is on treatments for specific amyloid-based diseases, this same

research can be bootstrapped into the SENS agenda. Once it has proven its

efficacy in Alzheimer's disease, senile cardiac amyloidosis, and type 2 dia

betes, the spinoff technology will allow for the rapid development of vac

cines for more obscure amyloid deposits that today may go nearly

unno t iced except in people with a hundred candles or more to illuminate

their birthday cakes.

The fact that these therapies have moved so quickly from the labora

tory into clinical trials (remember, results in mice with the first beta-

amyloid vaccine were reported in 1999, and it was in clinical trials by 2001)

suggests that we will be able to move even more rapidly in the future, when

the first anti-amyloid vaccines have passed through clinical trials and have

been successfully used in doctors' offices all over the world.

Eventually, I envisage a protocol to keep our bodies clear of extracellular


junk in which we might take a regular sequence of anti-amyloid vaccines,

not unlike the standardized series now given in regular succession over the

course of our childhood. The timing and frequency of administration of a

given vaccine would depend on how quickly its target builds up to levels

that impair function: we would get a "booster shot" of some every few

years, while others would be administered only a few times in each century

of a greatly expanded lifespan. Each time we took one of these vaccines,

our cells and organs would once again live and function free of a specific

species of molecular bindweeds, returning them to the literally unbound

potential of youth.

9

Year after year, ongoing chemical processes are shackling the

structural proteins of your body together, holding them back

from their vital jobs. Eventually, this leads to a familiar (and

ultimately fatal) range of age-related disabilities and diseases—

especially in the kidneys, heart, eyes and blood vessels. What if

we could break these chemical shackles, and thereby allow those

proteins to get back to work, as they did when you were young?

Scientists are making progress toward drugs that could

achieve just such a goal.

You're in the last hours before the big holiday feast, and the atmos

phere is heavy with the smells and emotional charge of the season. It's

been a long day in the kitchen—the oven running continuously, the ma

tron of the house trying to keep cool by leaving a window left slightly

ajar—and at last the hurry and stress are giving way to a more expectant,

eager sort of tension. The potatoes are mashed, the cranberry sauce has

been spooned into serving dishes, the sweet potatoes are being kept hot in

the oven, pumpkin pie is cooling on the windowsill. . . and now, a single

component of the meal dominates the cook's attention and the appetites of

her family.

Every fifteen minutes, like clockwork, for the last hour and a half, the

B r e a k i n g t h e S h a c k l e s o f

A G E

B R E A K I N G T H E S H A C K L E S O F A G E 1 6 5

turkey has been lovingly basted with its own fat, and perhaps a little honey;

now, to perfect the feast, the broiler is flipped on, to glaze its surface.

All the time that the turkey has been in the oven, complex chemical

processes have been imperceptibly proceeding—and now they accelerate.

Down at the molecular level, the high heat causes the sugars and fats to at

tack the proteins in the bird's skin. Molecular bonds are forged; new chem

ical products arise and are broken down; neighboring proteins are tied

together in shotgun marriages, tightening the outside surface of the turkey

and coating it with thick, gooey chains of linked proteins, fats, and sugars.

Finally, the deed is done. Mom flips the oven off and dons her oven

mitts as she calls to Dad to get the carving knife. The family looks on her

handiwork with eager eyes, gazing with hunger and appreciation at the

darkened, crispy, sticky, slightly toughened surface that the chemical mael

strom has made of the turkey's skin. Dinner is served.

I'm sure that you and your family have played out a similar script at

Christmas—or at Hanukkah, browning the latkes or sufganiyot. But, in a

profound sense, you have as much in common with the feast as you do with

the family.

Every day of your life, the same processes that are involved in the

browning of meats and other glazed or fried foods are insidiously at work

in your body. In your arteries. In your kidneys. In your heart, your eyes,

your skin, your nerves. At this very moment, in all your tissues, the sugar

that provides your body with so much of its energy is also performing some

unwanted chemical experiments, caramelizing your body through exactly

the same processes that caramelize onions or peanut brittle. Slowly but

steadily, unwanted bonding by sugars and fats handcuffs your proteins, in

activates your enzymes, triggers unhealthy chemical signals in your cells,

and damages your DNA. Aging you.

Make that: AGEing you. And I'm not just reminding you of my nation

ality by adding that final e.

The Way We AGE

The body relies on sugar as a key energy source. But, like any fuel, sugar can

only be "burned" by our cells because it is chemically reactive—and, again

like other fuels, that volatility can make it dangerous to work with. A d v a n c e d

Glycation End-products (or "AGEs," as they're appropriately called) are the

end results of the complex chemical processes through which the structure


of proteins is warped by sugars and other fuels. This same chemistry is the

cause of the "browning" you see when you roast a turkey, caramelize a

sauce, or pop a slice of bread into a toaster. AGEs accumulate in your tis

sues, leading to gradual loss of function, then disease, and ultimately an

early grave. AGEs transform the supple grace of youth into a "crusty" old

age, through exactly the same chemical processes by which they form the

crust on a loaf of bread.

The many chemical reactions, intermediates, and stable end products

of AGE chemistry have been the subject of an enormous amount of re

search, first in the food technology and chemical sectors and more recently

in biomedicine. Scientific study began with work by a food chemist named

Maillard in the 1910s and '20s, but it took until the 1980s for role of AGEs

in the complications that ravage the diabetic body to become a hot topic in

diabetes and aging research. Even now it's clear that we've only begun to

understand the furious promiscuity of this biochemistry and its impact on

the aging or diabetic body.

Though the details needn't concern us here, you will need to grasp the

outlines of how AGEs form if you are to understand the various strategies

that have been employed in the search for a way to shield us from their fos

silising influence. In the best-understood pathway (the main stream of the

Maillard reaction—see Figure 1a), a molecule of sugar opens its structure

and glues onto ("glycates") a protein molecule, forming a Schiff base. This

structure is relatively unstable, so the Schiff base will often spontaneously

fall apart. Sometimes, however, it will collapse into a more stable structure

called an Amadori product. Amadori products are much longer-lived than

Schiff bases. (This fact has long been exploited in a lab test that measures

levels of glycated hemoglobin or HbA1c, an Amadori product in red blood

cells, as an indicator of the average amount of sugar that has been present

in the blood over the course of the previous few weeks.)

Relatively stable though they may be, however, Amadori products are

still subject to the biochemical hurly-burly around them. They can there

fore be put through any number of further chemical transformations, such

as rearrangement or degradation of their basic structure, forcible insertion

of water molecules or removal of amino groups, or attack by free radicals.

Many of these changes lead to the formation of even more stable structures,

either directly or via highly reactive intermediate compounds such as

oxoaldehydes. These structures are stable enough, in fact, to be called "end

products"—they are the advanced glycation end products, or AGEs.

For our purposes, the important outcome of these processes is the

B R E A K I N G T H E S H A C K L E S O F A G E 167

Figure 1. The ways we AGE. (a) The "chemical" (Maillard) pathway; (b) The "metabolic" (triosephosphate) pathway; (c) Sources of methylglyoxal.


Figure 1. (continued).

formation of AGE cross-links, a subset of AGEs in which proteins that are

already working with one arm tied behind their backs because of glycation

become shackled to a second, neighboring protein.

AGEing happens much more quickly in people with diabetes than in

the rest of the population, partly for the simple reason that diabetics' blood

sugar levels are higher: In any chemical reaction, a higher concentration of

an active agent will tend to increase the rate of its interactions with its tar

gets, provided those targets are plentiful. But AGE cross-links also accu

mulate in people with normal blood sugar levels, and it's quite clear that

they are responsible for much of the pathology and increased vulnerability

to the insults of daily life that accompany "normal" aging.

Browning to Death

The cross-linking of proteins is similar, at both the molecular level and the

functional level, to the processes that cause windshield wipers to lose their

flexibility. For people who don't have diabetes, the most life-threatening lo

cus of the ensuing stiffening of the tissues is the cardiovascular system.

AGE cross-links slowly impair the youthful elasticity of your heart and

blood vessels, making them rigid and unyielding. The resulting hardening

of the arteries is in large part responsible for the increase in systolic blood

pressure that everyone suffers with age. (Systolic pressure is the first of the

two numbers that you get from a blood pressure reading, like the "110" in

"110 over 80.") Meanwhile, the AGEing of your heart impairs its capacity

either to contract to pump blood through your body, or to expand in order

to fill up with that blood in the first place. The combination of these two


factors increases the workload on the heart, ultimately leading to one of

several forms of heart failure if nothing else kills you first. The same lack of

plasticity also means that your blood vessels become less able to withstand

the constant surges of blood that course through them: they become brittle

and eventually break under the pressure like old rubber bands, one poten

tial result of which is a bleeding stroke.

And the damage caused by AGE cross-links extends well beyond the

cardiovascular system. They shackle proteins all over the body, accumulat

ing with age in tissues as diverse as the tiny blood vessels in your eye and

the supporting myelin sheaths of your nerves. Everywhere they occur, AGE

cross-links impair the functioning of those proteins, contributing to age-

related dysfunction, disability, and death. In your eyes, they accumulate on

the crystallin proteins that make up the structure of the lens. AGEd lens

proteins stop allowing light to pass through them, leading to the brown

pigmented spots in the lens that we know as cataracts. The combination of

this browning with several effects at the cellular level is why age and dia

betes are the major risk factors for this, the single greatest cause of vision

loss worldwide.

And that isn't the only way in which AGEs contribute to vision loss.

Elsewhere in the eye, AGEs contribute to diabetic retinopathy (vision loss

in diabetics linked to damage to the fine blood vessels feeding the light-

absorbing tissues at the back of the eyeball), to age-related macular degen

eration, and possibly also to open-angle glaucoma.

The kidney, too, suffers badly from AGE assault—again, especially

among people with diabetes. Diabetic damage is the single biggest cause of

kidney failure in the United States, and a third of all patients who find

themselves in the dialysis ward got there because of their diabetes. Indeed,

the severity of kidney disease in diabetics tracks the level of renal AGEs,

which cross-link the proteins of the kidneys' biological filter material and

trigger an inflammatory process that leads the body to overcompensate by

growing too much replacement tissue, in a sort of out-of-control wound-

healing response. The net effect of these two processes is a buildup of

something similar to scar tissue in the kidney, which accumulates to levels

that literally squeeze the tiny blood vessels where filtration is supposed to

occur, reducing the amount of filtering surface available and leading to in

efficient screening of materials in the blood—as if you had glued a coffee

filter paper back on itself before running the machine, leading to a ground-

filled mess when the water starts to back up.

AGEs also contribute to diabetic neuropathy, the debilitating damage


to the nerves that is suffered by so many diabetics. The severity of this dis

ease can vary, but the most common symptom is an unremitting version of

the experience one has after a temporary, pressure-induced reduction in

blood flow to the hands or feet (i.e., when the extremity is said to be

"asleep"): a sensation of "pins-and-needles," pain, or numbness in the af

fected limbs, along with some loss of control or clumsiness in their use.

People with diabetic neuropathy also lose some of the unconscious control

by their nervous systems of functions such as the regulation of the heart's

rhythm, the digestive process, the bladder, and erectile function; they also

often suffer dizziness, and nausea that may extend to vomiting. Whether

AGEs play any role in similar, more subtle defects in nerve function with

age in otherwise healthy people is unclear, but it seems likely.

Comparisons of the rates of accumulation of cross-links in the tissues

of slower- and faster-aging species, and of slower- and faster-aging individ

uals within a species, suggest that AGEing plays an important role in aging

per se, not just in specific diseases or the complications of diabetes. Both

the rate of age-related buildup of one of the more easily measured AGEs

(pentosidine) and the related toughening-up of the proteins in skin or tail

tissue are inversely associated with the maximum lifespan of different

mammalian species. This means that the more slowly a species ages, the

more slowly its collagen is stiffened by AGEs (see Figure 2). Likewise, calo

rie restriction—which is, as I've mentioned in previous chapters, the best-

studied way to slow down aging in mammals—slows these processes down;

and in fact, higher rates of tissue AGEing have been shown to predict early

death in individual calorie-restricted animals. 1 In our own species, studies

show that even within the "normal" range (i.e., at values well below those

typical of people with diabetes), higher blood levels of either glucose itself2

or of the Amadori product HbA1c 3 are associated with a higher risk of

death from all causes.

A drug that would slow down or reverse the accumulation of AGEs

would thus help people with a wide range of diseases and disabilities. It

could potentially improve, or even cure, problems as wide-ranging as the

gradual increase in blood pressure over a lifetime; the terrible kidney,

Figure 2. Maximum life span as a function of AGE formation rate. Redrawn.4


nerve, and visual complications of diabetes; and several forms of heart fail

ure. And it could also help us to address a major contributor to aging itself.

This idea didn't just pop into my head recently, of course: a variety of

schemes to reduce the tissue AGE burden have been explored over the

years, and many of them have even reached relatively advanced clinical trial

status. Yet, despite years of work, none of these treatments has been shown

to be safe and effective enough to find its way into the drug arsenal of any

developed country. The obstacles that have plagued their development and

limited their usefulness represent yet another case study in the problems of

trying to deal with age-related damage by tinkering with the complex bio

chemistry of life.

Listening to Parmenion

"Sugar P i l l s "

The fact that AGE cross-links are often ultimately the result of sugar mole

cules acting like a glue, gumming up our tissue proteins, immediately sug

gests one possible solution to the problem: just lower people's blood sugar

levels, and you'll reduce the formation of Schiff bases (see Figure 1) in their

bodies and thereby lower their AGE burden. Of course, this has long been

the major focus of diabetes management, and in the 1990s, two massive and

widely cited scientific studies—the Diabetes Control and Complications

Trial (DCCT) and the UK Prospective Diabetes Study (UKPDS)—were

hailed as the clearest proof yet of the effectiveness of this strategy when

taken to its limits. These two studies showed that when diabetics take strict

steps (aggressive use of blood-sugar-lowering drugs and regular feedback

in the form of frequent blood sugar testing) to keep their blood sugar un

der very tight control, they are at greatly reduced risk of developing the ma

jor complications of the disease. The DCCT, in particular, showed that—as

compared with the standard of care at that time—a regimen of intensive

blood sugar control could reduce a diabetic's risk of developing nerve dis

ease by close to two-thirds, diabetic kidney disease by about half, and dia

betic retinopathy by an astounding three-quarters.

The results of these two studies were trumpeted around the world—by

their government sponsors, by patient advocate organizations, and by phar

maceutical companies looking to boost sales of glucose-lowering drugs. The

plan was to encourage doctors to prescribe these drugs to patients whose


blood sugar control was in the range that made them safe by previous stan

dards but demonstrably at risk based on the new data, and also to increase the

doses taken by people with worse control who were already using the drugs.

The benefits that would accrue to patients as a result of such a surge in

drug use seemed to be clear-cut: people with diabetes all over the world

would enjoy miraculous improvements in the quality and length of their

lives through dramatic reductions in their risk of blindness, nerve damage,

and kidney failure. But when scientists actually assessed the overall quality

of life of people who had undergone the intensive therapy regimens in the

trials, the results were surprisingly gloomy. Despite the fact that more ag

gressive treatment had reduced the risk of all major diabetic complications,

the intensive-therapy patients enjoyed no improvement in their net well-

being as compared to people who had been assigned to standard care. 5 , 6

Many factors probably contribute to the lack of clear-cut benefits from

aggressively lowering blood sugar levels. While diabetic complications

clearly have a negative impact on quality of life, the drugs used to lower

blood sugar also come with costs that are not included in the sticker price.

People on such medications tend to gain weight, which reduces their qual

ity of life—both directly, and by increasing the risk of other diseases such as

osteoarthritis. Many patients also find that sticking with the rigid schedule

of injections and finger-prick tests required to keep up with these regimens

imposes real restrictions on their lives, which some studies report con

tributes to depression, frustration, isolation, or troubles at work.

And finally, constantly trying to push blood glucose even into the "nor

mal" range carries with it the risk that blood sugar levels will drop too far,

leading to a "hypoglycemic crisis" whose consequences can range from

dizziness to a coma. This is of particular relevance to normal aging. If push

ing blood sugar levels down is a mixed bag for diabetics, you can see that it

would be a decidedly dubious solution to the AGE problem for the rest of

us, in whom the wiggle room between our normal blood sugar levels and a

hypoglycemic crisis is much smaller, making the potential benefits more

limited and the risks higher.

And even if we could safely bring our blood sugar down to the lowest

possible safe level, we'd be quite far from a complete solution to the AGE

problem. All of us must maintain some level of glucose in our blood as an

energy source, and some percentage of that glucose will always wind up re

acting with tissue proteins, leading to cross-linking.

And on top of that, not all AGEs are even derived from glucose. Blood

fats ( tr iglycerides) can also cause the cross-linking of proteins, particularly if


there's a high level of oxidative stress; this is the chemistry that underlies

the browning of a turkey skin as it roasts, even without a sweet, syrupy

slather on its surface. As with blood sugar, diabetics usually have high

triglyceride levels, and even many nondiabetic people would benefit from

having their triglyceride levels brought down; but triglycerides also resem

ble blood sugar in being indispensable to normal function, so there's only

so far that such a strategy can be safely pursued.

Less Is More . . . Is Worse

And that's not all: attempts to control levels of both these early precursors

of AGEs, even by nonpharmacological means, can have perverse metabolic

consequences.

For instance, one established effect of very low-carbohydrate diets of

the Atkins type is to bring down both triglyceride levels and the body's to

tal exposure to carbohydrates, so some advocates have hypothesized that

these diets would reduce a person's AGE burden. Unfortunately, it turns

out that the metabolic state that these diets induce (the notorious "ketosis")

has the unfortunate side effect of causing a jump in the production of the

oxoaldehyde methylglyoxal, a major precursor of AGEs that is also, ironi

cally, produced within the cells of diabetic patients when they are f o r c e d to

take in more glucose than they can immediately process (see Figures 1b and

1c). A recent study tested the size of this effect in healthy people who suc

cessfully followed the first two phases of the Atkins diet for a month, and

who had the ketones in their urine to prove that they were sticking to the

diet. These previously healthy people suffered a doubling of their methyl

glyoxal levels, leading to concentrations even worse than those seen in

poorly controlled diabetics. 7 Like other oxoaldehydes, methylglyoxal is far

more chemically reactive than blood sugar (up to 40,000 times more reac

tive, in fact), and is known to cause wide-ranging damage in the body, of

which AGE cross-links are but one example. This potentially makes the

Atkins diet a recipe for accelerated AGEing, not a reprieve from it.

"Radical" Proposal—-Lukewarm Results

Even before the counterintuitive results of the DCCT came out, it was obvi

ous that a blood-sugar-lowering strategy would not be a complete solution


to the AGE problem. The body needs blood sugar and fats as fuels, and yet

no level could be so low as to eliminate all cross-link formation: at best, low

ering the concentration of glucose and triglycerides would delay the in

evitable. So some scientists turned their attention elsewhere, to

cross-link-inducers whose harmful role in the body is less ambiguous.

One such AGE-prevention strategy is the use of high doses of antioxi

dants to bring down free radical levels. As you can see from Figure l a , free

radicals can accelerate the conversion of some AGE precursors into certain

specific full-blown cross-links—a phenomenon called glycoxidation. Based

on the effect of adding free radicals to proteins and sugars in test-tube ex

periments, glycoxidation can be predicted to hit diabetics with a double

whammy, because in addition to the excessive levels of blood glucose and

fat, the impaired metabolic state of diabetes also causes an overproduction

of free radicals in victims' cells. Put the two factors together and you have a

potentially synergistic interaction. Also highlighting the importance of free

radicals in AGE formation is the fact that birds have sky-high blood glu

cose levels that would rapidly kill a human, yet generally live around ten

times longer than mammals of the same size; part of how they get away with

this is probably by having really good control of oxidative stress.

If glycoxidation were a major reason for diabetics' high levels of AGE,

then sopping up their excess burden of free radicals with antioxidants might

considerably reduce the cross-linking of their tissue proteins, resulting in

longer life expectancy and reduced risk of crippling complications. And

many studies carried out in laboratory rodents have supported this expecta

tion: dosing them with various free radical quenchers typically reduces the

cross-link burden in their tissues considerably, cutting back on the incidence

and severity of diabetic kidney, nerve, and even retinal damage.

When antioxidants were tried as an anti-AGE therapy in humans,

however, the results were disappointing. The effects on AGE levels and

symptoms were minor or nonexistent—and even when benefits were ob

served, the effect was almost exclusively confined to the most severe cases

of the disease, with more typical diabetics getting no relief. 8 , 9 , 1 0 We now

know that there are a couple of major reasons for this. First, human dia

betes causes a much less severe increase in oxidative stress than is suffered

in the rodent version of the disease, as can be seen by comparing the levels

of molecules damaged by free radicals in the two species' skin. This lower

free radical load makes glycoxidation a less important factor in human dia

betics' AGE chemistry, and thus weakens the potential benefit of reducing

its impact.


But another, more general reason for the lack of efficacy of antioxi

dants as an anti-AGE therapy is the sheer riotous promiscuity of the highly

reactive precursors of AGE cross-links. One highly revealing animal

study 1 1 illustrates the point. Diabetic rodents were given diets fortified with

different antioxidant supplements (vitamins or green tea extracts), and the

impact on the animals' AGE burden was assessed by comparison with both

healthy animals and diabetics given unsupplemented chow. To tease out the

biochemical pathways involved, scientists measured levels of substances

produced at several different steps across the spectrum of the glycoxida

tion process, from initial glycation events to the creation of specific AGE

cross-links—some of which are created by glycoxidation, and others by

straightforward glycation, i.e., without the involvement of free radicals.

As previous rodent studies had shown, antioxidant treatment did exert

some benefits on diabetic complications. Equally predictably, the treat

ments had no effect on the initial glycation of proteins, since the window of

opportunity for free radicals to work mischief in AGE chemistry opens up

further along in the process (Figure 1a). But the researchers got a surprise

when they began looking at actual cross-links. Antioxidant supplements

had no effect on the levels of those AGEs whose formation doesn't require

free radicals, of course—but the intervention actually increased the levels of

the two glycoxidation-derived AGEs, so that diabetic animals receiving

green tea extracts actually wound up with more total cross-linking than

those who simply suffered the "natural" course of the disease.

This remarkable result yet again illustrates the hopeless complexity of

the tangled skein that is metabolism. The precursors of these AGE cross

links don't simply disappear when they aren't hit by free radicals—they

have to go somewhere—and when much of the excess oxidative stress was

relieved by antioxidant supplementation, these precursors began to build

up until they spilled over into one of the alternative pathways of cross-link

formation. It was the same effect you see in traffic jams when a main traffic

artery is cut off: a few drivers may indeed just turn their cars around and

go home, but most of them turn off onto the local side streets, creating

secondary traffic congestion in hitherto sleepy residential neighborhoods.

Collateral Damage

The best-understood pathways of AGE cross-linking are fundamentally

random events, not too far removed from what happens in the browning of


food, or in a test tube. The fuels of metabolism, dissolved in your blood or

in the fluid inside your cells, randomly bump into tissue proteins; depend

ing on factors like temperature, concentration, and the presence of transi

tion metals and free radicals, a series of chemical events may occur; and if

they happen in just the right order, an AGE cross-link will form.

But some AGEs result more directly, from the regulated activity of

metabolic processes. One recently identified example is the enzyme

myeloperoxidase, which is used by macrophages to kill bacteria by gener

ating toxic hypochlorous acid. It has been shown that hypochlorous acid,

in the presence of the protein building-block serine, can itself induce

AGE-type cross-linking, independent of the usual fuel chemistry of sugars

and fats. 1 2

If myeloperoxidase were only ever activated to kill bacteria, it might be

a relatively unimportant source of AGEs in people living in the developed

world who don't have chronic infections (although the number of such

people is much higher than is generally appreciated). But, as we saw in

Chapter 7, macrophages don't just attack bacteria: they also become

aggravated—and crank up their myeloperoxidase activity—in their short

sighted efforts to clear trapped cholesterol from your arteries. Some scien

tists now believe that myeloperoxidase is probably a major contributor to

the high levels of AGE found in the atherosclerotic foam cells of nondia-

betic people.

While reducing excess myeloperoxidase activity might be desirable at

the sites of atherosclerotic plaque, we probably could never lower its activ

ity pharmacologically without also impairing our ability to defend ourselves

against bacteria. As people with AIDS know, when your immune system is

suppressed, you're not just at risk from relatively rare bacterial killers like

tuberculosis: you can be felled by infections that most of us shake off be

fore we have even the beginnings of symptoms. Moreover, and surprisingly,

one study found that animals bred to produce something like human ather

osclerosis, but lacking the ability to produce myeloperoxidase, showed

more severe atherosclerosis than animals with normal activity, again illus

trating the frustrating complexity of metabolic processes. 1 3

The Drug That Failed

Okay, so trying to lower the levels of the ultimate AGE precursors, like

glucose and fat, is difficult—and also unsafe, because they are essential


biological fuels. Soaking up free radicals and sequestering transition metals

is of limited effect because there are so many alternative routes to AGE

formation.

But an overview of Figure 1 may suggest a much more attractive target:

oxoaldehydes. For one thing, these reactive compounds are present at

much lower concentrations than blood sugar or triglycerides, meaning that

you would only have to knock out relatively few molecules to lower the to

tal level in the body by a significant proportion: methylglyoxal, for instance,

is several thousand times less concentrated in the blood than glucose. On

top of this, oxoaldehydes are very virulent molecules (as I mentioned ear

lier, methylglyoxal is up to 40,000 times more prone to attacking tissue pro

teins than glucose is), so that each molecule you take out of circulation is

much more likely to translate into the prevention of a cross-link in the wait

ing. Oxoaldehydes also play their role in cross-link formation relatively late

in the process, leaving fewer alternative pathways by which an AGE might

form if they could be soaked up. And in contrast to sugars, which are es

sential molecules for which there is a limit beyond which lowering their

concentration in the blood becomes life-threatening, oxoaldehydes are fun

damentally toxic molecules, so that one should be able to reduce their con

centration drastically without doing any harm to the body.

Thus, if trying to lower AGE formation with antioxidants or blood-

sugar medications is like launching a wide-sweeping crackdown on an entire

crime-plagued neighborhood, a drug that mops up oxoaldehydes would be

like springing a carefully targeted police raid on known members of a brutal

criminal gang.

For a long time, a drug called aminoguanidine (trade name Pimagidine)

seemed poised to fulfil this promise, revolutionizing the treatment of dia

betes and perhaps landing the first serious punches on the Mike Tyson that

is biological aging. The drug enjoyed a lot of buzz in the scientific literature

on diabetes, as well as in some of the commentary on life extension in pop

ular magazine articles and Internet discussion groups, because its clearest

mechanism of action was precisely its ability to mop up oxoaldehydes.

Over the course of many years, researchers put aminoguanidine to the

test—first in test tubes filled with AGE precursors and mixtures of cata

lysts, then in cell cultures, and eventually in animal studies. And at nearly

every juncture, hopes for the drug continued to rise. In diabetic rats, it low

ered AGE formation in the cells of the retina and reduced the maladaptive

overgrowth of the blood vessels feeding them. In dogs, it prevented the loss

of the retinal blood vessel cells and the associated accumulation of dead


blood vessels through which blood had stopped flowing. It also kept both

species' hearts and blood vessels more flexible.

Somewhat less consistently, aminoguanidine showed promise against

other complications of diabetes. It reduced the total level of kidney tissue

that was so cross-linked as to be indigestible by strong acids, and prevented

much of the thickening of the kidney's filtration machinery that accompa

nies diabetes in rats—although it was unable to affect the course of the dis

ease in dogs. Further, diabetic rodents (but not baboons) given the drug

exhibited less loss of blood delivery to nerves, and improved ability to con

duct nerve impulses.

Most important for those of us looking for interventions against AGEs'

role in the degenerative processes of aging, aminoguanidine even seemed

to reduce heart and kidney AGE levels (and the resulting loss of those or

gans' function) in animals that were suffering from purely age-related AGE

accumulation rather than diabetes.

After a few small human studies designed to test for any obvious toxicity

seemed to go well, the company that had patent control over aminoguani

dine for use as a drug for diabetes attracted the attention of the biotech giant

Genentech, which partnered with them to launch two full-scale clinical trials.

Each one was to involve about six hundred people with the beginnings of di

abetic kidney disease, in medical centers spread out all over North America.

The first trial (ACTION I) recruited people with type I (autoimmune) dia

betes; the other trial (ACTION II) was to involve patients with the more

common type II (late-onset) diabetes, which usually develops as a result of

lifestyle, albeit sometimes overlaid on genetic vulnerability. Ambitiously, pa

tients in both trials were to be well medicated to control both blood sugar

and blood pressure before being put on aminoguanidine, so that differences

between the groups would be entirely the result of the test drug's direct anti-

AGE effects.

But when ACTION I was completed in 1996, the best spin that one

could put on the results would be to say that they were disappointing. On the

positive side, risk factors like blood pressure, LDL ("bad") cholesterol, and

triglycerides went down in people who had received the drug. And some

crunching of the data suggested that the drug might improve some indicators

of kidney function. Plus, in a tiny subgroup who had been tested before and

after the trial, diabetic damage to the retinas seemed less serious in patients

taking aminoguanidine than those taking placebo—though these observa

tions were suspect, because they were made as an afterthought after the trial

had been shut down rather than being part of its original design. 1 5


What the study was supposed to show was a direct effect on kidney

health, as measured by a standard laboratory test for kidney function—and

the data just weren't strong enough to support that conclusion. The raw

numbers looked, on their face, better in aminoguanidine users than in the

placebo group, but the difference was so small relative to the number of pa

tients in the trial that it seemed likely to be a statistical fluke, like getting

"heads" in six out of ten coin tosses instead of the expected five.

Worse: while the benefit attributable to aminoguanidine was dubious,

the risks associated with the drug seemed undeniable. Along with signs of

an overactive (and possibly damaged) liver and strange flu-like symptoms

that went away when they stopped using the drug, a few people taking

aminoguanidine developed signs in their blood of an autoimmune disorder,

which—in three patients taking the higher dose—was associated with a

form of highly inflammatory kidney disease that leads to complete loss of

kidney function in a matter of just weeks or months. Two of the three pa

tients who developed the disease progressed to end-stage kidney failure.

Fortunately, this apparent side effect was caught early in the trial, and the

safety committee accordingly introduced a monitoring program, after

which no one was allowed to progress into clinical signs of the disease.

A FATAL R E S E M B L A N C E

Even now, we still don't know for sure what caused aminoguani-

dine's severe toxicity, which had not been observed in animal stud

ies. But there's a good guess—and if it's correct, it makes

aminoguanidine yet one more case study in how trying to repress

the dark side of metabolic processes so often has repercussions.

What made aminoguanidine a promising AGE-blocking drug

was its mechanism: the sopping-up of oxoaldehydes. These sub

stances are in a class of chemical compounds called carbonyls:

organic molecules with a carbon atom double-bonded to an oxy

gen atom. This structure makes many carbonyls highly biologically

active, which is why oxoaldehydes are such relentless shacklers of

bodily proteins. Of course, metabolism relies on the harnessing of

highly active compounds to carry out the biochemistry of life—

and so it's hardly surprising that many essential biological mole

cules also feature prominent carbonyl groups.


The problem is that aminoguanidine can't necessarily tell one

carbonyl-bearing molecule from another. That might be expected

to cause it to sop up some essential carbonyl-bearing molecules

along with toxic ones like oxoaldehydes. In fact, we know that it

does so in at least one case: vitamin B6. As a result, animals given

aminoguanidine can easily develop a deficiency of this vitamin

indistinguishable from simply putting a subadequate supply of it in

their diet.

Damningly, a blood pressure drug called hydralazine, which

brandishes the same carbonyl-trapping hydrazine surface that

aminoguanidine's business end uses to neutralize oxoaldehydes, is

well known to cause a lupus-like autoimmune disorder, the first sign

of which is the appearance in the blood of the same antibodies

observed in the aminoguanidine users in ACTION I.

If a drug as promising as aminoguanidine can't safely prevent enough

AGE damage to improve the health of diabetics, you can be sure that it

won't do much for the basically healthy among us. Because the concentra

tions of blood sugar and fats are much lower in people without diabetes,

the buildup of AGE is much slower, and thus harder to slow down to a de

gree that causes a measurable change in their health. Thus, it would take a

lot longer for any potential benefits to accrue, whereas the risks remain at

the same high levels for each individual year of use.

Indeed, a study published after aminoguanidine's withdrawal from clini

cal development 1 7 appears to show that even the initial reports of a reduction

in age-related AGE cross-linking in nondiabetic rodents were specific to the

strain of rat used in early studies (which is particularly susceptible to kidney

disease). Other strains showed little or no benefit from lifelong aminoguani

dine administration.

These are just a few illustrations of the known or anticipated ways in

which the mechanisms underlying cross-link formation undermine our

ability to prevent AGEing. This nightmare of biochemical complexity is so

elaborate as to cause even the most dedicated puzzle enthusiast to snap

pencil in two and go to bed in frustration; it should raise serious doubts

about the wisdom of continuing to invest resources in seeking new ways to

interfere with such a poorly understood, multiply-branching network of

pathways (Figure 1). In the pell-mell of the body's biochemistry, a certain


quantity of AGEs is simply inevitable, and trying to prevent enough cross-

linking from happening to have a real impact on the stiffening of our tis

sues, without somehow disturbing essential metabolic processes, may

ultimately be futile.

If you've read the preceding chapters of this book, you probably have a

pretty good idea of the sort of strategy I'd like to see used to deal with the

problem of AGEs, whether in diabetics or in "normal" aging. Don't mess

with blood sugar. Don't try to block free radicals. Don't go chasing after

ways to outsmart metabolism. Don't try to prevent AGEs from forming at

all. No, the anti-aging engineer's solution should be to allow metabolism to

proceed in its infamously messy way, and then to remove full-blown AGEs

themselves before they build up enough to impair tissue function, robbing

us of youthful flexibility of heart and sinew and increasing our risk of death

and disability.

In this case, however, I am not playing the role of visionary, so much as

of cheerleader. At least two companies have developed such drugs and

tested them in animals. One of them has undertaken several clinical trials

already.

A SENS Serendipity

In the decade since Drs. Tony Cerami and Peter Ulrich had first suggested

that the cross-linking of proteins by glycation might be the link (pun in

tended) between high blood sugar levels and the complications of diabetes,

they had spent a lot of their time working on ways to do something about it.

They had played key roles in the development and early testing of

aminoguanidine, but well before the failure of ACTION I they knew that

much stronger molecules would be required to help two specific groups of

people with quite different AGE-inducell disabilities. On the one hand, di

abetics whose disease had progressed so far that they had already suffered

a lot of cross-linking would be quickly approaching the threshold at which

their total level of cross-linking would begin to result in disability and

death, and would therefore require much more effective interventions than

would people only in the early stages of the disease. And on the other hand,

many people who suffer with AGE-derived diseases such as hypertension

and heart failure have normal blood sugar levels. In these people, the pre

cursors of AGEs are present at much lower levels and are thus are much

harder to intercept: it's like trying to shoot down a single bird in the sky,


whereas taking on AGE precursors in diabetics is like sighting one of the

incredible flocks that once blacked out the sun in the early days of Europe

an colonization of the Americas, into which hunters could fire off buckshot

without even bothering to aim.

So in late 1991, Cerami arranged for a summit at their labs at the Pi-

cower Institute for Medical Research in Manhasset, New York. The meet

ing brought together himself, Ulrich, several other Picower staffers, and

scientists working for a company Cerami had helped form named Alteon,

to brainstorm on new ways to inhibit AGE formation.

Analysis of what was believed about the chemistry and products of

these reactions had already led many researchers to conclude (correctly) that

reactive carbonyls (like oxoaldehydes) would be important potential sources

of AGE cross-links, and thus targets for anti-AGE drugs. This was exactly

the rationale for the development of aminoguanidine. Ulrich saw that, theo

retically, a lot of the body's AGEs might be formed from a class of reactive

carbonyls known as Amadori diones and the related Amadori-ene-diones.

These molecules would form when Amadori products broke down: car-

bonyl groups would join hands across the gulf of adjoining proteins, result

ing in an alpha-dicarbonyl link—specifically, a type of alpha-dicarbonyl

called an alpha-diketone link. On chemical grounds, such a link would not

be expected to remain intact for long—but it wouldn't just disappear, either.

Most likely, Ulrich thought, it would rearrange into a more stable, final

structure—a molecular marriage which only death would part.

If that were true, Ulrich could see one potential path to the develop

ment of novel anti-AGE interventions. The body has enzymes that break

down at least some kinds of dicarbonyl compounds, and many of these en

zymes share in common the incorporation of the vitamin thiamine. Re

search by Ukrainian scientists in the mid-1980s had shown that molecules

in the same chemical family as thiamine (called thiazolium compounds)

break linkages of the same chemical type, albeit embedded in organic

chemicals rather than as AGEs in tissue proteins. The inclusion of thiamine

in so many of these enzymes, combined with the mechanism of other thia

zolium compounds, suggested that thiamine was the essential feature to all

of them, like the common head shape of different brands and sizes of

Phillips screwdrivers. The active core of the incorporated thiamine would

get an electrochemical grip on the carbonyls in the enzyme's target mole

cule, whereupon the enzyme would twist its shape, opening up and tearing

the bonds apart.

Ulrich wanted to design a new molecular "tool" that would do the


same splitting job with the dicarbonyl bonds in Amadori diones, eliminat

ing their cross-link-forming potential. Starting with the concept of a

thiamine-like "business end," the assembled scientists began throwing out

suggestions on how different kinds of molecular "levers," "swivels," and

"sprockets" might behave, predicting their interactions with Amadori

diones from their structures. Ulrich stood at a blackboard, drawing out

their proposals.

Finally, they came up with a basic template of a class of molecules that

might be expected to cleave the kinds of bonds present in the Amadori-

diones that they believed would probably be found in the body. Then they

threw together a variety of specific variations on the theme by tacking on

various "limbs" to the core "backbone" structure.

At the end of a marathon session, the Alteon scientists took the results

of their work back with them for preliminary testing. At Alteon, Dr. Jack

Egan assigned several junior scientists to synthesize test quantities of each

of their various candidate molecules, and also to cook up large batches of

some model Amadori diones. From there it was a straightforward series of

simple experiments: pipette small quantities of the candidate molecules

into test tubes full of the AGE precursors, and see if they could inhibit

their conversion into more permanent structures.

As it turned out, however, "straightforward" did not mean "quick."

After having run dozens of tests at different concentrations and still not

having nearly exhausted the range of experiments they wanted to do, Egan

was looking for a faster way to run the experiment. In collaboration with

scientist Sara Vasan, he devised an alternative method. He wasn't sure this

new method would work, but they would certainly save a lot of time and ef

fort if it did.

At first, the new procedure seemed to work fine: a lot of the work was

moved from the old protocol to the new one, and soon they had accumu

lated a broad enough sample of data to expect that the answers they

needed would be buried somewhere inside their mountain of notes. Vasan

gathered the results together and began writing them up for internal analy

sis and possible publication.

And at first, it seemed that they had their results: the test tubes con

tained varying amounts of AGEs, suggesting that the compounds had in

hibited their formation from their precursors to varying degrees. But a few

of the results seemed to be wildly out of step from the main body of work,

with the levels of the expected reaction products being well in excess of

what could be accounted for by the small variations in concentrations and


other factors as compared with other, similar tests using the same com

pound. The chemistry just didn't make sense.

Embarrassed at having to ask her supervisor, and afraid that she had

simply overlooked something or that she or one of her coworkers had im

properly performed the experiments, Vasan showed the results to Egan. He

agreed that the results didn't make sense, and they began going back to the

original lab notebooks to double-check the results.

It didn't take long to see that the outliers were coming quite consis

tently from experiments using the new, faster protocol. Egan and Vasan

went back over the protocol, looking for a flaw—the kind of "garbage in,

garbage out" error that makes an accounting program tell you that you owe

twice your annual income in taxes. Eventually, they found a mistake in the

last few steps in the initial production of the model Amadori diones them

selves. At one key point, the correct procedure is to put a halt to the reac

tions occurring in the test tube, preserving the compounds that have been

produced. Instead, the protocol was allowing further reactions to occur,

generating alpha-diketones instead of freezing them at the precursor phase.

They had, in effect, been "overcooking" their biochemical soup, generating

mature alpha-diketone linkages and leaving few or no intact Amadori

diones available against which Ulrich's carbonyl-busters could be tested.

But while this was clearly a mistake, Egan and Vasan doubted that it

was the only one, because it couldn't fully account for the anomalous re

sults of the inhibition tests. The results of those experiments had initially

looked right, because after the inhibitors were mixed in with their test com

pounds, their quick-and-dirty assay methods had detected the remnants of

shattered Amadori diones floating like molecular flotsam in the test tubes.

But how would such chemical debris have been produced if there had been

no Amadori diones present for the thiazolium inhibitors to destroy?

It was then that it hit them. The explanation was staring them in the

face; indeed, the chemistry would've been obvious, if they hadn't walked

into the experiment with a preconceived understanding of the reactions

that they would be observing. Because they could see the broken carbonyl

groups that would be expected to be left behind after the thiazolium com

pounds had torn apart the Amadori-diones that they thought were present

in the test tubes, Egan and Vasan had been assuming that the presence of

those broken bonds meant that the inhibitors were doing what they had

been designed to do. But what if they were doing something else entirely?

What if the carbonyl groups that they were detecting in the final samples

were the remnants of alpha-diketone links that had been produced in error


during the generation of the test compounds, and then torn apart by their

model drugs?

Egan felt no "Eureka!" moment of insight, however—and not only be

cause he still hadn't figured out how those alpha-diketones could have per

sisted long enough to be attacked by Ulrich's model drugs. No, his mood was

neither intellectual satisfaction nor ongoing curiosity, but a sinking recogni

tion that they had been wasting their time. The Amadori diones would have

to be resynthesized, probably using the original, time-consuming protocol,

and the inhibition assays run over again.

There was no sense in covering things up. Egan contacted Cerami and

explained the situation, apologizing for the wasted time and emphasising

that it was all going on Alteon's bill.

Egan initially thought nothing of the questions that Cerami asked

about the experiment: scientists are nothing if not inquisitive. But it did be

gin to seem odd as the doctor pressed him for more and more arcane de

tails of the procedure, the reasoning underlying his conclusions, and even

speculations about how the thiazolium compounds might have reacted

with the alpha-diketones. Unfortunately, Egan had no real idea how such

an interaction might have led to his observations: he was a bench scientist,

not a medicinal chemist. What a relief, he thought: Cerami's curiosity seems

to have gotten the better of his frustration with this setback.

Cerami hung up the phone and leaned back in his chair, his mind rac

ing. Was he missing something? Did he dare to believe what Egan was

telling him—or to accept the implications?

Trying to calm his trembling fingers, he dialed Peter Ulrich. Impa

tiently, he waited for his partner to pick up the phone. Finally, the click of a

lifted receiver. "Ulrich," said the familiar voice at the other end.

"Peter?" Cerami said, keeping his voice steady. "Can you explain to me

how one of these compounds could break an AGE cross-link?"

Reverse-Engineering Serendipity

Over the course of the next few weeks, Ulrich worked backward from

Egan's protocol and Vasan's results, developing a tentative scenario under

which mature AGE compounds based on an alpha-diketone linkage could

be broken by their new thiazolium compounds. Finally, he thought he had

the chemistry right.

If the result held, then they were really on to something. Thanks to the


laboratory flub, Picower and Alteon were at the center of not one, but two

breakthroughs in AGE biochemistry: one theoretical, and one of enormous

potential medical significance. First, the result implied that alpha-diketone

AGEs might be stable enough to persist in the body long enough to con

tribute to tissue stiffening without any further chemical alteration. And sec

ond: they had unwittingly designed a class of molecules that would not

merely prevent AGE from forming, but actually buzzsaw their way through

them.

The biomedical implications were startling. Imagine being able to take

patients whose bodies were already extensively riddled with cross-links,

and to give them a drug that would break the AGE apart. AGEd tissues

would be rejuvenated. Arteries would dilate outward in response to the

pulsing tide of blood; hearts would fill with the incoming flow; even skin

could become flexible again. It was just the solution that one would dream

of for advanced diabetic cases, or for people whose AGEs had built up be

cause of time, not high blood sugar. The market would be enormous.

The hard-nosed chemist in Ulrich brought him back from this vision to

the steps that lay between him and its realization. For starters, Alteon

would have to run the previous experiments again, monitoring the reac

tions at each step to provide evidence to support the theoretical chemistry

that he had outlined to explain the original result. Additionally, everything

that they had done thus far was with an AGE that had been cooked up in a

beaker: he still didn't know whether any alpha-diketone AGE (let alone the

specific molecule that Vasan had accidentally produced) ever actually

formed in the body at levels sufficient to impair tissue function. And then

there was the question of whether his test compounds would be able to re

produce in human subjects what they were doing under glass: the body's

detoxification machinery might metabolize them into inactive forms, or it

might be impossible to take enough of the stuff to have any effect.

The first few questions were answered by a more careful, intentional

repetition of Egan's and Vasan's initial experiments, which seemed to con

firm all his hopes. The results of these studies were consistent with the

hypothesis—that the predicted AGE was in fact formed from the model

Amadori diones, and that it persisted long enough to react with his thia

zolium compounds, which did indeed appear to sever the cross-link at the

alpha-diketone bridge. And based on the observed results, one particular

thiazolium compound—a chemical known as N-phenacylthiazolium bro

mide (PTB)—was an especially effective wrench with which to pull these

AGEs apart.


But the fact that PTB severed a bond in an artificial AGE didn't prove

that it would break any of the cross-links that actually tie up the arteries,

hearts, and other organs of aging and diabetic humans. At this point, it was

time for Cerami, the more medically minded member of their tag-team, to

get more actively involved. The two decided to put PTB through a graded

series of increasingly challenging tests using more and more lifelike model

systems, working their way step by step from single cells up to functional

and molecular investigations in living, breathing animals.

The Manacles Fall Away

These necessary studies were again farmed out to people working under

Jack Egan at Alteon, whose lab scientists first confirmed PTB's ability to

cut through AGE using isolated, cross-linked proteins and tissues. With

each successful jump over an experimental hurdle, their optimism grew,

until they were ready to move their work into the living laboratory of dia

betic laboratory rodents. When Egan's team injected the animals with their

new compound, the results were again positive: levels of glycated proteins

bound to the animals' red blood cells dropped by over a third in the first

week, and kept dropping, going down to half of the original level after

three weeks and to just 40 percent by the end of the month. It really looked

as though they were on to something.

With that evidence to hand, Alteon scientists began giving PTB injec

tions to rodents with hearts, kidneys, and arteries hardened by AGEs, ac

cumulated over a normal healthy lifetime or in the fast-forward mode of

diabetes. Here the real excitement began to build, as PTB continued to live

up to expectations, restoring supple performance to cardiovascular systems

that had previously lost their youthful flexibility, instead of just slowing

down an inevitable decay as aminoguanidine had done. Structurally, the tis

sues of treated animals were softer and more elastic, stretching out like rub

ber bands fresh out of the pack, and readily melting away when doused

with digesting chemicals; functionally, their hearts were expanding to fill

with incoming blood like new balloons, and blood coursed through their

arteries without the large backward-rippling "echoes" of pulse that are

characteristic of old blood vessels.

They did have one problem, though, which was that PTB is too unsta

ble to succeed as a drug for human use: by the time a pill had made its

way through digestive system and the complex chemistry of the body's


drug-metabolizing processes, too little would be present to have a mean

ingful therapeutic effect. But Ulrich was not going to give up on so promis

ing an agent, and with a bit of work he and the Alteon chemists were able

to develop a variant on its basic structure that was not only more stable but

more active: 4,5-dimethyl-3-(2-oxo-2-phenylethyl)-thiazolium chloride. For

convenience, Alteon first shorthanded this mouthful to ALT-711 (because it

was ALTeon's 711th compound); later, the compound would be rebranded

to the more marketable alagebrium.

A drug with the ability to cleave AGEs that had already formed in the

body would have applications in diabetes as well as in a wide range of dis

eases of aging, but regulators only approve drugs for one specific indication

at a time. Wanting to carve out as exclusive a niche for the drug as they

could, Alteon strategists set their sights on developing alagebrium for con

ditions that were not already being successfully treated with existing medi

cines, and that would be expected to respond uniquely well to their new

treatment.

One of these diseases was isolated systolic hypertension (ISH), the kind

of high blood pressure in which a person's systolic reading (again, this is

the first of the two numbers that you get from a blood pressure cuff, like

the "110" in "110 over 80") is high, even though their diastolic pressure

(the second number) is fine. Systolic pressure is a measure of how much

pressure is applied to the artery wall by the surge of blood into the vessel as

the heart contracts, whereas diastolic pressure is the baseline pressure in

the arteries at rest (technically, at "diastole."). Hormonal and other factors

can actively tighten up the blood vessel, keeping the pressure inside the ar

tery high even during diastole; such effects raise blood pressure irrespec

tive of the intrinsic flexibility of the artery as a tissue. But when systolic

pressure is high despite a normal diastolic pressure, it's a sign that the ves

sel itself has become stiff, unable to expand to accommodate the incoming

rush of blood from the heart.

This nonatherosclerotic "artery hardening" is not just a concern in

people with a diagnosis of isolated systolic hypertension. As people push

past middle age, arterial stiffness becomes an increasingly powerful predic

tor of heart disease and heart attack, and indeed comes to override many

conventional risk factors like cholesterol and blood pressure when it comes

to risk of actual cardiovascular events (heart attacks and strokes). FDA and

other regulators don't recognize this "normal" effect of the aging process as

a "disease" for which they'll approve a drug, so Alteon knew that they

could never get official sanction for the use of alagebrium to treat these


people; but they also knew that, once the drug had been proven to buzz-

saw through the constricting manacles of AGEs in the artery, restoring

flexibility and opening up the vessels to the systolic flow, they could vastly

expand the market for it by quietly encouraging its unapproved ("off-

label") prescription to untold thousands of aging people with age-related

arterial stiffening.

Another disease whose victims don't get much benefit from existing

drugs and would be expected to respond more specifically to an AGE-

breaker is diastolic heart failure (DHF). The more common, systolic form

of heart failure occurs when the heart's lower, pumping chamber loses the

strength to push out enough of the blood that it receives from the upper

chamber to keep the body supplied with oxygen and nutrients. But about

a third of heart failure patients have a perfectly normal capacity to pump

blood; their problem is that the same chamber can't expand sufficiently

well to take in the required volume of blood in the first place, so that the

body's needs remain unmet even after it squeezes out nearly all of the load

that it first takes in. The result is the same—the body's tissues are starved

for blood—but the cause is different, and treatments that admirably ad

dress systolic heart failure leave the bodies of DHF patients still crying out

for critical fuels. While the underlying loss of the heart's filling capacity

can be the result of a variety of factors, many cases of the disease are asso

ciated with AGE stiffening of the heart. Again, an AGE-breaking drug

would be uniquely suited to restoring healthy functionality to these peo

ple, and trials showing that it could restore the elasticity of old hearts

would also spark interest in its use by large segments of a "healthy" but

rapidly aging population.

Alagebrium proved its mettle quickly, doing everything that PTB could

do and more. Studies showed that alagebrium in the drinking water of lab

oratory animals could deliver the same kind of restoration of heart and ar

tery flexibility that PTB had elicited only via injection, and more easily. And

there were things that alagebrium could do that PTB had never been able

to pull off. For example, PTB had cleaved some of the AGEs that had ac

cumulated in the kidneys of diabetic rodents, but not enough to restore the

organ's functionality. Treat the same animals with alagebrium, and not only

does their kidney collagen become more soluble, but also the fibrotic dam

age to their kidneys recedes, and the organs get better at filtering proteins

out of the blood, preventing their spillover into the urine.

And rodents were only the first order of mammals to benefit from

alagebrium. Alteon and their collaborators soon proved that alagebrium


could rejuvenate the hearts and blood vessels of dogs and monkeys. These

studies were much more informative about the prospects for alagebrium as

a true anti-aging drug than anything that had come before, for a couple of

reasons. First, they were carried out in animals that were undergoing "nor

mal" aging, whereas the rodent alagebrium studies had used severely dia

betic animals. Second, dogs and nonhuman primates enjoy longer lives,

and the extra years give the forces of aging more time to induce the same

kinds of pathological cardiovascular system changes that are observed in el

derly humans, making them better models of human disease from a clinical

and theoretical point of view.

As in elderly humans, older dogs' heart chambers stretch less to ac

commodate incoming blood than do those of younger animals, leading to

reduced filling with blood and a simultaneous increase in the pressure

within it. In other words, old dogs suffer from mild diastolic heart failure.

When older animals were given a moderate dose of alagebrium for a

month, their hearts became about 42 percent more flexible, as demon

strated by an increase in the volume of blood taken up in the absence of

any increase in blood pressure inside the chamber. The contrast was even

more marked when the volume of blood delivered into the heart pump

chamber was increased using drugs: just weeks before, this treatment had

even further widened the performance gap between old and young dogs in

cardiac flexibility, but after alagebrium treatment their hearts were nearly

as elastic as those of the young controls. 1 8

The results seen in our fellow primates were even more striking. 1 9 In

2001, scientists from Alteon—working in collaboration with researchers

from the National Institute on Aging (NIA) who were studying the effects

of aging and calorie restriction on nonhuman primates, as well as with NIA

specialists in cardiovascular medicine—published the results of a study on

the effects of alagebrium in the cardiovascular systems of rhesus monkeys.

Their test group was old, but "healthy" as biologically old monkeys go—

and in particular, free of diabetes.

At the beginning of the study, the monkeys' arterial flexibility was as

sessed, as was the degree to which their heart chambers ballooned outward

during their blood-filling (diastolic) phase, as a measure of the flexibility of

the tissue. The monkeys then received alagebrium every other day for three

weeks, after which their tissues were retested every few weeks for the next

nine months.

Surprisingly, there was no measurable effect on blood pressure—

systolic or diastolic. But three weeks after treatment, and even more pro-


foundly at the six-week mark, their cardiovascular systems' tissues had

clearly undergone a restoration to more youthful elasticity. Using one rough,

easy-to-administer test of arterial flexibility, their arteries had become

an astounding 60 percent more pliable; a more direct assay revealed a

25 percent improvement. At the same time, their hearts were also opening

up more easily: they were taking in 16 percent more blood during the dias

tolic phase, and other measures of cardiac function at least partially de

pendent on improved diastolic filling likewise improved after alagebrium

treatment.

Alagebrium wasn't expected to prevent new bonds from forming be

tween sugars and proteins, so it was no surprise that the withdrawal of the

drug was followed by the loss of these gains once the gradual molecular

manacling of the monkeys' tissues was no longer being counteracted by an

even more rapid breaking of those bonds. Within a few weeks of the peak

of their alagebrium-inducell return to more youthful suppleness, the mon

keys' arteries were once again as stiff as they had been in the initial run-up

to the study. Their hearts held onto their gains a little longer than the arter

ies, but then they too began tending to fall back into their old recalcitrance.

Quitting the drug didn't leave the monkeys any worse than they had been

to begin with—but it was clear that the AGE links being broken by alage

brium could be quickly reforged. The implication is that users of alage

brium would have to take the drug on an almost continual basis in order to

keep enjoying their newfound arterial plasticity.

But that didn't much dampen anyone's spirits. The results of these

studies marked a clear landmark in the development of alagebrium. Toxic

ity was low; no serious side effects had been observed; and the promise of a

new treatment for stubborn diseases was clear.

It was time for human trials.

From Darkness, Light

The first human alagebrium trial, published in the prestigious American

Heart Association journal Circulation in 2001 , 2 0 looked like the tentative

beginning of something big. Seventy-three older men and women with

signs of vascular stiffening had their blood pressure and arterial flexibility

assessed and were then p l a c e d at random into one of two groups. For two

months, two-thirds of the patients took alagebrium in pill form; at the same

time, the remainder received a look-alike pill with no active ingredient as a


placebo control. At the one-month mark, and again at the end of the trial,

their parameters were reassessed.

The results were not altogether clear, allowing for a range of interpre

tations, but the study was understood to be preliminary by its very nature,

and most researchers were willing to give the drug the benefit of the doubt

based on the remarkable results achieved in the animal models. Systolic

and overall blood pressure had gone down in both groups, probably be

cause of an unusually strong "placebo effect" in the group getting the

dummy pill: the influence of the power of belief on the actual state of the

body, which is a notoriously important confounder in hypertension studies.

Whatever the reason, the result was that the drug conferred no clear ad

vantage in blood pressure results. At the same time, the arterial stiffness of

the people taking alagebrium seemed to have improved in comparison to

the placebo group using two different measures, but there were technical

objections to the method used in one of these assays and the nature of the

comparison between the groups also made its results less than decisive.

Subsequent trials, however, have provided results that, in aggregate, al

low us to draw firmer conclusions—and, unfortunately for Alteon, they

suggest that alagebrium will never be approved by regulators for clinical

use. Over a thousand patients with systolic hypertension, diastolic heart

failure, systolic heart failure (with and without an associated, compensatory

overgrowth of the heart's main pumping chamber) and even erectile dys

function, as well as some healthy individuals, have been treated with alage

brium in early clinical t r i a l s , 2 1 , 2 2 , 2 3 , 2 4 and while the results provide enough

evidence to suggest that the drug is safe and is breaking AGEs in these pa

tients, the effect is clearly insufficient to have much impact on actual func

tion. The results on diastolic function in the heart have not been impressive;

the benefits in improved arterial flexibility have not been clear-cut; and lit

tle, if any, effect on hypertension per se has been observed. Often the main

objective of the trials has not been achieved, with the benefits mostly ac

cruing in less-important markers of the disease process that are not clearly

linked to clinical outcomes (cardiovascular disease, heart attack, or stroke).

Moreover, the benefits that have been observed have not been cleanly tied

down to any particular dose of the drug. This is paradoxical because one

might well expect that, in a drug that breaks AGEs, benefits would increase

with the dose: more drug ought to mean more broken AGEs and therefore

more youthful cardiovascular systems.

To date, the sum of the data from the animal studies clearly suggests

that alagebrium can break AGEs; the question is why this benefit is not


translating into improved vascular and cardiac health in human users as

they do in so many other species.

Some critics hold that alagebrium is not actually an AGE breaker after

all, but an AGE inhibitor, just as Ulrich and his colleagues originally de

signed it to be. There is a certain superficial plausibility to this view, but

these arguments can't stand up against the irrefutable fact that, in animal

studies, alagebrium doesn't just slow down the development of complica

tions in diabetic rodents on prevent the AGE-related tissue stiffening of the

cardiovascular system in normally aging dogs and monkeys: it reverses

them. A drug that only inhibited the cross-linking of tissues would be able

to reduce the rate at which new cross-links would form, and thereby slow

down the degeneration of cross-linked tissues—but it would not have the

kind of rapid restorative effects that have been elicited by alagebrium.

The fact that the tissues of alagebrium-treated animals become inflexi

ble again so quickly after withdrawal of the drug also seems to weigh in

against the suggestion that the drug is actually just reducing AGE forma

tion, since the underlying cross-links are clearly reforming much more rap

idly than they did over the many years that were required for their initial

buildup. This observation suggests that the severing of the alpha-diketone

bridge in these AGEs exposes a highly reactive carbonyl group, which soon

sticks itself back onto an adjacent proteins. Because of the ongoing break

ing of other cross-links, users of the drug keep ahead of this problem in

"two steps forward, one step back" fashion—but take it away, and they un

dergo a rapid return to their old, AGEd state.

What about the inability of researchers to find alpha-diketone cross

links in the body? The reason is almost certainly that these structures are,

ironically, a bit too easy to destroy. The difficult thing about designing an

AGE-breaker drug is not that there's any lack of chemicals that can break

apart a given cross-link; the problem is to come up with something that

won't also tear normal, healthy proteins to shreds in the process. The com

mon ways of finding AGEs in the body involve soaking a tissue sample in

strong acids and examining whatever's left over. This technique catches the

most extremely hard-to-destroy AGEs, such as pentosidine, but wipes out

all trace of more delicate cross-links.

It was long suspected, and has in recent years been confirmed, that the

crudeness of such assays introduced serious distortions in AGE research.

In the last decade, new methodologies have been developed to uncover

AGE cross-links in tissue through a painstaking process of breaking down

the normal, healthy chemical bonds in a tissue almost one by one, leaving


behind only abnormal chemical linkages such as AGEs. Using these tech

niques, researchers have proven that the AGEs we previously thought to be

the most abundant are actually just the most resistant to the chemical

carpet-bombing that had previously been used to drive them out of hiding.

The most readily-assayed AGEs (like pentosidine) are in fact relatively rare

in the body (and therefore make little contribution to the overall state of tis

sue stiffening), while other cross-links that are much more common (and

therefore impose a much larger total protein-shackling burden on living tis

sues) remained invisible to our testing methods.

I believe that this is the explanation for our inability, thus far, to iden

tify the molecular targets of alagebrium. The predicted structure of alpha-

diketone cross-links is such that they would be relatively easy to break

apart: indeed, you'll recall that this is why Peter Ulrich originally didn't

think that they would even hang around for long enough to be worthwhile

pursuing as a drug target.

In turn, the unfortunate difference in the functional impact of alagebrium

treatment in human patients, as compared with lab rodents, dogs, and mon

keys, may be the result of alpha-diketone cross-links simply being a much

more common kind of AGE in those species than in our own. It's clear that

there are differences in the metabolic pathways underlying AGE formation

amongst the species. For instance, as we saw above, diabetic rats' bodies

suffer much more oxidative stress than ours do in response to the disease.

This should affect not only how AGEs are generated, but which specific

cross-links are formed: structures whose formation involves free radicals

will probably be a much bigger burden in rat tissues than in human ones.

Another reason to think that alpha-diketone cross-links may be less im

portant to our own species than to others is the simple fact that we're much

longer-lived than those other organisms. Long-lived, recalcitrant AGEs like

pentosidine are very hard for the body to break down, so they tend to ac

cumulate pretty linearly with age: the result is that, while longer-lived or

ganisms accumulate them more slowly than shorter-lived ones, they wind

up with higher absolute levels of such AGEs by the time they end their

lives, simply because they've had many more years to accumulate them. So,

if you look at Figure 2, you'll see that at fourteen years of age, an extremely

"elderly" dog has about forty units of pentosidine in a milligram of its col

lagen, while a minipig of the same age—but with half of its maximum life

expectancy still ahead of it—has only fifteen units. A monkey could possi

bly live for forty years, and at age ten it has only accumulated five units of


pentosidine. A human, with a maximum life span of more than hundred,

has fewer units still. Yet by age sixty, when AGE cross-links are beginning

to weigh in seriously on a person's chances of surviving for another year,

human skin is burdened with some fifty units of pentosidine cross-linking

its proteins per milligram of collagen—more than any of the shorter-lived

species had time to accumulate.

Now: remember that, in contrast to a supremely tenacious cross-link like

pentosidine, alpha-diketone cross-links—the kind broken by alagebrium—

are predicted to be relatively fragile as AGEs go, so the level of these cross

links is an equilibrium between rather rapid formation and breakage. Like

all AGEs, the decline of metabolic control of fuel as we age would lead

to an increase in the rate of its formation with age—but its relative ease

of elimination should allow the body to largely keep on track of this in

crease, leading to a much slower rate of accumulation than the stubborn

pentosidine.

The net result of this would be that, late in life when AGE-inducell

stiffening is becoming rapidly fatal, the contribution that alpha-diketone

cross-links would make to the total burden of AGE (and thus, to loss of

needed flexibility) in a tissue would be less in a long-lived species like ours

than in a monkey or a dog (let alone a mouse), for the simple reason that we

would have accumulated so much more of the more resistant types of AGE

than shorter-lived creatures ever get the opportunity to do. Thus, an alpha-

diketone breaker like alagebrium would, even if highly effective at its spe

cific molecular task, leave a much greater burden of other cross-links

behind than would be the case in model organisms, resulting in much less

effective restoration of youthful tissue plasticity.

Alagebrium and Beyond

So where does this leave alagebrium in the SENS agenda? Clearly, the lack

of clear-cut clinical benefits in humans indicates that this drug itself will not

play a major role in the reversal of cross-link damage in our tissues. Its

value, instead, is as a proof-of-principle: it shows us that AGEs can be

cleaved in the body, and tissues regenerated, long after metabolism has

done its dirty work in binding our proteins together. What will be required

is a new generation of AGE-breakers that slice through more abundant

AGEs, and thus free us of the structures that are really holding our tissues


immobile. Such agents will yield the same kind of benefits in humans that

alagebrium does in animals—benefits first demonstrable in diabetes, ISH,

and diastolic heart failure, and ultimately in aging itself.

It's important to stress that no single drug will totally save us from tis

sue cross-linking. As we've seen, glycation leads to the formation of many

different AGEs, each with a distinct structure. Drugs that will sunder any

given AGE will probably leave most others untouched: no one molecule

will be able to sever all of these distinct intermolecular linkages. Therefore,

as we saw with amyloids in Chapter 8, we will need to develop a range of

drugs, each of which cleaves either one specific cross-link structure or at

most a small family of similar ones.

But the eventual need to develop drugs to break a number of distinct

AGE structures doesn't mean that we can't effectively stop AGEs from

contributing to the aging of our hearts, arteries, and other tissues until we

have a solution for all such cross-links in hand. The insight underlying the

"engineering" school of anti-aging biotech tells us that we don't have to

solve all of our problems at once to intervene in the process: We can "reju

venate as we go," taking one challenge at a time.

To see why this is so, remember that the molecular damage underlying

aging begins accruing while we are still in our mothers' wombs, yet we re

main youthful well into our thirties: it takes many decades of these insults

before the amount of damage is sufficient to exert a functional impact on

our bodies. Until this threshold level is reached, a given form of aging dam

age is essentially harmless to us in itself.

Therefore, to restore more youthful flexibility to a tissue, we do not

need to sever all the various kinds of AGE cross-links in our bodies, but

only the ones that make the greatest contribution to the stiffening of our

tissues. For practical purposes, rejuvenation will be effected as soon as we

can cleave a sufficient proportion of the AGE structures in our bodies to

keep the total amount of cross-linking beneath the threshold level that ac

tually impairs tissue function.

Once we have a drug that breaks a given kind of cross-link, we will be

free of its baleful influence. The solution, by its nature, will not be once and

for all: we will undergo a new course of treatment once every few years or

decades, taking the drug for a few weeks or months—long enough to break

enough AGEs to leave our tissues as flexible as they were in our youth.

These cross-links will immediately begin to build up again, of course—but

we have the luxury of letting them do so until that critical threshold level is

approached again. (Note that this scenario assumes that the AGE-breaker


leaves the broken AGE in a chemically inert state, which alagebrium evi

dently doesn't do to alpha-diketones; if the broken AGEs are reactive, the

drug will have to be taken continuously.) However, the first effective AGE-

breaker will not solve the entire problem of AGEs. It will probably reach

the clinic first by virtue of targeting the most abundant AGE, but it will

surely not break all AGE species. Thus, other AGE cross-links will con

tinue forming in our bodies unabated, albeit at a slower pace. These cross

links will first reach pathological levels once our lives have been extended

for long enough that they stiffen our tissues on their own as much as they

and the first-targeted AGE jointly do in a currently normal lifetime.

So, yes, we will need to identify these AGEs as well, and to develop

treatments that target them. But the important point from an engineering

perspective is simply that this doesn't emerge as an actual biomedical prob

lem until the first wave of anti-aging (including anti-AGEing) treatments

has extended our lives quite a bit on its own. The first breaker of an abun

dant AGE will buy us the time to identify such AGEs and to develop new

treatments that will free us from them in turn.

Eventually, we will develop a lifelong regimen of AGE-breakers not

unlike the childhood vaccine schedule today, under which we will receive a

series of specific cross-link-severing drugs, each administered on its own

cycle of years, decades, or perhaps even centuries, based on the rates and

sites of their targets' formation in the body. But to achieve the first great

leap forward in restoring the suppleness of youth to AGEd tissues, we need

only prioritize the development of cross-link breakers that will carve their

way through the cross-links that cause us clinical problems within a

presently normal lifespan.

The above section only discusses AGEs, but similar logic applies right

across the SENS spectrum. I'll be discussing it in more detail in Chapter 14.

Know Your Enemy

Today, for the first time in history, we are in the position to design such

drugs on a rational basis. Just over a decade ago, when Peter Ulrich and the

Alteon chemists were doing the work that ultimately led to the develop

ment of alagebrium, they were working in the dark. They didn't even know

for sure that the types of AGE that they were targeting actually existed in

the body—they were simply guessing, from studies carried out in test tubes,

that such links might form and contribute to stiffening of living tissues. But


the new enzyme-based methods that I mentioned earlier now allow us to

slowly take tissues apart at the molecular level, layer by layer, revealing the

presence and levels of pathological cross-links in our body, exposing our

previously hidden opponents to the light of science.

Researchers who have taken the time to develop and apply these new,

painstaking procedures to aging human tissues have given us reliable tar

gets on which to fix our crosshairs: a complex structure called glucosepane,

which was only identified using these new techniques in 1999, 2 5 and prob

ably another AGE called K2P, which is prominent in the lenses of our eyes

and possibly other tissues. 2 6 Glucosepane is the single most important con

tributor to the body's AGE burden known to date, tying up as much as one

out of every five molecules of the key structural protein collagen in old,

nondiabetic humans. Glucosepane levels are around one hundred times as

high as that of any other AGE that had previously been found in collagen

or the lens. A drug that could free our tissues from these AGE shackles

would have a much larger impact on total cross-linking burden than alage

brium does, and would thus bring our tissues much closer to their full

youthful flexibility and functionality.

Today, while we will still use the same sort of blackboard molecular en

gineering that Ulrich and his copanelists did in the early '90s to design new

AGE-breakers, we can fashion molecular bolt-cutters that are precisely

tooled to break specific AGEs, whose exact molecular structures are in our

possession, and whose presence in our bodies and biomedical significance

as major contributors to the total cross-linking of our tissues with age are

certainties.

We also have the advantage of having faster screening tools in our pos

session. We can use software to simulate the behavior of AGE-breakers, and

to automate the generation of variations on a core molecular theme. We can

put robotics to work to synthesize thousands of ampoules of candidate drugs,

and use mechanized, high-throughput techniques to assay their effects

against a known culprit in the loss of elasticity in our hearts and other tissues.

Being able to look at glucosepane's exact chemical structure gives us an

other advantage in developing its nemesis that Ulrich no doubt wishes he

had had so many years ago. The hard part of developing a glucosepane-

breaker for clinical use is not identifying chemicals that can destroy it: as we

saw earlier, the acids we used in our old AGE-assaying techniques did a re

grettably excellent job of it. The problem is to create molecules that will do

it selectively, without damaging healthy biomolecules that share the same

vulnerability exploited by the would-be drug. Having reconstructed glu-


cosepane's molecular identity, biochemists can now see just how wide is the

latitude they have in designing molecular shears for it.

Fortunately, this latitude may be very wide indeed. The structure of

glucosepane is so different from any functional structures in ourselves or

other mammals that a drug that selectively targets them should be harmless

to any molecule that is supposed to be found in our bodies.

As I've explained, the resulting glucosepane-breaker should be the first

in a series of AGE-cleaving drugs that we will need to unbind our proteins

from their molecular shackles. Then we will have achieved for the first time

in humans what was observed just a few years ago in dogs and monkeys

treated with alagebrium. Old hearts will open wide again, free to fill with

life-giving blood. Hardened old arteries will once again readily expand in

response to the surge of the blood of life. The stiffened, inflexible tissues of

the aged will move with the suppleness of youth. The absurdity and outrage

of a body tying itself into molecular knots will come to an end, and we will

bend and flex within and without as children in the jungle gym of life.

10

P u t t i n g t h e Z o m b i e s t o R e s t

As we age, we build up an increasing collection of "death-

resistant" cells in our tissues. This is one part of our

biochemical program to avoid cancer: shutting down the activity

of potentially cancerous cells before they can cause trouble.

Unfortunately, rather than simply remaining silent and harmless,

such cells still manage to damage surrounding tissue through

chemical signals gone awry. But by taking a leaf from the

world of new, targeted cancer therapies, we can foresee the

development of safe, effective methods to remove these senescent

cells from the picture.

So far, I've mostly been talking about specific forms of damage that

happen at the molecular level to our cells and their components, and how

we can restore functionality to our cells and tissues by undoing, or render

ing harmless, that damage. But there are a few cases where the aging body

accumulates cells that are damaged in such a way that they don't just stop

contributing to the economy of the body, but actually become toxic to the

system that supports them.

I've already discussed one such case, back in Chapter 5: cells that have

been taken over by mutant mitochondria. When mitochondria lose the

ability to process fuels, as a result of mutations to their internal DNA, what

ultimately causes us harm is (in my view) not the resulting failure of these

organelles to carry out their job. Rather, it's the maladaptive way that their

P U T T I N G T H E Z O M B I E S T O R E S T 2 0 1

host cell alters its metabolism in order to survive that failure. This meta

bolic alteration keeps such cells limping along by dumping oxidative stress

outside their membranes and on to far-flung areas of the body.

At first glance, one might think that the best thing for the body to do

with such cells would be to kill them off, thereby saving the rest of the body

from their toxic influence. But the nature of the specific cells that develop

this problem makes any attempt at simple removal fraught. The most no

table case, arguably, is skeletal muscle. The design of muscle means that de

stroying a single muscle cell-like structure will snap the entire fiber in

which it's embedded. Loss of muscle cells to aging (rather than to disuse) is

already a major source of age-related frailty; we can't afford to add to that

problem by killing off more of them in self-defense.

So in this particular case, as I described in Chapter 6, what seems to

make the most sense is to find a way to preserve and restore normal meta

bolic activity in affected cells in the face of their colonization by mutant mi

tochondria, instead of killing them.

However, there are plenty of other cases in which the costs of destroying

a toxic cell are negligible, and the benefits clear and direct. Everyone is fa

miliar with one such case—cancer—and no one disputes that destroying

cancer cells is unambiguously positive. I won't be discussing cancer in this

chapter, however (except for the applicability beyond cancer of some exist

ing anti-cancer treatments), because that disease poses such unique chal

lenges that I've devoted a whole separate chapter (Chapter 12) to it. Instead,

I'll focus on three cell types that pose a much less catastrophic threat than

cancer, but that still make a substantial collective contribution to age-related

descent into illness, frailty, and death. From what I can see, there is no rea

son to attempt to rehabilitate these cells: it seems best that they, like cancer

cells, be destroyed. I'm choosing to discuss them together because of the

similarity of the threats that they pose and of the strategies that I advocate

for dealing with them.

Attack of the Clones

The decline of the immune system is one of the most deadly effects of ag

ing. Infections that young people shake off as mere inconveniences are

commonly fatal in the biologically old. Influenza, for instance, puts 114,000

Americans into the hospital each year, and flu and flu-related illnesses claim

the lives of about 51,000. But the disease burden is dramatically skewed


Figure 1. Aging vulnerability to pneumonia and flu. (a) Hospitalization rates by age, Connecticut, 1993-1997 (females). Redrawn.1 (b) Death rates by age. Redrawn from CDC data.2

toward people who have previously suffered the ravages of aging (see Fig

ure 1). Deaths from influenza and influenza-associated pneumonia are al

most unheard-of in adults until the seventh decade, after which rates climb

exponentially. In the United States, over 90 percent of all deaths from the

two diseases are in people over sixty-five years of age.

We could, of course, do something about the death toll through vacci

nation. But not much: between 30 percent and 75 percent of older people

fail to respond to flu shots, compared with just 10 percent of young adults.

Add to this the facts that we sometimes vaccinate against the wrong strain

of the flu, limiting the effects of even successful vaccination. There are var

ious reasons for the weakening of the immune system that happens with ag

ing, some of which are ultimately downstream effects of aging elsewhere in

the body (like the systemic increase in free radical stress spread by mutant

mitochondria). But one of the most profound—and unexpected—factors

underlying our inability to mount a defense against infections that young

P U T T I N G T H E Z O M B I E S T O R E S T 203

people shrug off without ever suffering a sniffle is, believe it or not, a form

of immunological overcrowding.

State of the Forces Report

There are two main branches to the immune system. One is the so-called

innate immune system, whose "innateness" comes from the fact that its job

is so general that it doesn't have to "learn" to identify a specific enemy. Its

job is similar to that of regular soldiers on patrol in a demilitarized zone,

trying to maintain order but unsure of who might be the enemy, ready to

confront anything suspicious-looking that they happen upon. There seem

to be very few changes in the innate immune system with aging, and those

that have been reported appear to be secondary to other aspects of aging

and age-related disease (and we'll be discussing a few of those later on), or

to factors that are common in the elderly but not a result of biological aging

at all, such as vitamin and mineral deficiencies.3

The other main branch is the adaptive immune system. The adaptive

immune system is more like a division of highly trained special forces units,

each of them expert in waging targeted, tactically sophisticated warfare

against specific enemies. This branch is responsible for the ability of the im

mune system to learn about invaders—and, thus, for the effectiveness of

vaccines.

Within the adaptive immune system are the B cells and T cells. B cells

are mostly responsible for defending us against pathogens like bacteria and

parasites that are purely foreign to the body, and that can therefore be tar

geted directly for destruction. B cells recognize specific markers (antigens)

on the surface of such an invader that reveal it as foreign, and churn out an

tibodies to them. I talked about antibodies back in Chapter 8, in discussing

vaccination as a way of clearing out amyloids: they destroy alien cells by

binding to the antigens of the organisms they're intended to fight, acting

like homing beacons that attract "missiles" fired by other components of the

immune system, or blocking receptors and other proteins that are needed

for the pathogen's survival.

By contrast, cytotoxic T cells (also called CD8 cells because of the char

acteristic receptor they bear) are responsible for rooting out the enemy

within: cells that are native to the body but that have now been turned

against it, such as cancer cells or cells hijacked by viruses. (There are other

types of T cell in addition to CD8 cells—more on them later.) CD8 cells


also use antigens to target their foes, but because the targets are hiding in—

or in the case of cancer, as—the body's own cells, CD8s don't get the

chance to catch the pathogens' calling cards on their own surfaces, and

can't target the invaders directly. Instead, CD8 cells pick up antigens on the

surfaces of host cells that have been infected by a pathogen, or more often

on other cells in the immune system that act like reconnaissance agents,

scooping up copies of the antigen left in the wreckage of cells destroyed by

the enemy and reporting their findings back to CD8 cells to alert them to the

threat. Having spotted enemy colors, CD8 cells seek out and destroy the in

fected host cells, eliminating their threat to the rest of the body.

The problem, once again, begins with the body's need to balance com

peting priorities in its metabolic processes—and to do so in the face of lim

ited resources. On the one hand, it's critical that the immune system be able

to identify and fight off infectious agents that it's never seen before, so it

needs to have a reserve of CD8 cells that are ready to respond to new

threats, "learn" about their key antigens, and then mount an attack; these

are called naive CD8 cells. On the other hand, the process of ferreting out

an enemy that you don't recognize takes time, during which an invader

could gain a life-threatening foothold in the body, so we also have a com

plement of memory CD8 cells—veterans of old immunological battles,

which remember the enemy that they defeated and stand ready to identify

and fight them off again.

B a l a n c e d Budgets

This would be fine if we could keep on hand as many T cells as we might

like, including plenty of naive cells and large contingents of memory cells

specific to each of the many pathogens that our body has racked up in its

rogues' gallery over the course of the years. But producing and maintaining

these armies is a resource-intensive investment, and as with everything else,

the body's "budget" for the immune system is limited. To avoid going into

deficit on its "military" spending, the body maintains a strict policy of bal

a n c e d budgets—a limited amount of "immunological space" (as it's been

called) for the entire T cell population in aggregate. The immune system

ruthlessly maintains a cap on the total number of naive and memory cells

combined in the body at any given time, although the specific makeup of that

population is in constant flux, shifting dynamically as the body responds to

the threat of the moment.


When this system is working well—as it does in most young people—it

is the very model of the kind of flexible, low-cost, highly mobile, well-

trained army that many of today's generals and world leaders dream of con

structing. During an infection with a particular pathogen, there is a rapid

redeployment of forces to meet the threat on the ground. Whether it's mem

ory cells mobilizing against an enemy that they've seen before, or naive cells

uncovering and mounting an attack on a brand-new threat, CD8 cells ap

propriate to the enemy at hand expand their numbers, dividing rapidly in a

process called clonal expansion, and then fan out, identifying and destroying

cells bearing the foreign protein markers against which they specialize. (This

use of the term "clone" is one of several in biology; it must not be confused,

let me stress, with the popular nonscientific use of the word. I'll have more

to say about the various meanings of "cloning" in the next chapter.)

But once an enemy has been defeated, maintaining huge numbers of

CD8 cells whose only mission is to wage war on a foe that has just been

driven away would be a waste of limited resources. With the body's iron dis

cipline on its immunological budget, it can't afford to have so much of its

army be specialized for combating just one opponent if that enemy isn't ac

tually in the process of waging a campaign. So the body initiates a rapid and

massive scaling back of these cells, ordering the bulk of the veterans to en

gage in a carefully orchestrated self-destruct program (apoptosis), after which

it can rebalance its deployment of forces to a more generic defensive posture.

But a few veterans of the recent conflict are kept on after the cessation of hos

tilities as memory cells, on the lookout for signs of a renewed attack from the

invaders that they know so well. The small numbers required to maintain the

body's vigilance against a known enemy make this expense quite tolerable, so

that the cost of keeping these cells on the payroll never puts significant strain

on the "budget" of the immune system. That's the plan, anyway.

Old Soldiers Never Die . . .

Unfortunately, this model of fiscal and military discipline only works well for

infections that can be totally eliminated from the body. It begins to break

down when the body faces enemies that it can fight to a standstill but not

quite wipe out entirely. One class of such enemies is viruses of the herpes

family: not just the infections commonly called "herpes" (herpes simplex of

the mouth or genitals), but also Epstein-Barr virus (the one that usually

causes glandular fever), varicella zoster (which causes chicken pox), and


most especially a little-known infection called cytomegalovirus (CMV). All

these viruses can be beaten back enough to put an end to active, sympto

matic disease, but they are never completely defeated. A few copies of the

virus continue to lurk hidden in some hard-to-reach corner of the body, dor

mant and out of sight of the immune system, waiting for the day when the

tissue or the body as a whole is in such a weakened state that they can flare

up again. In fact, the very name "herpes" is taken from the Greek herpein,

"to creep," in reference to their ability to sneak about the body while they

await conditions favorable to their reactivation.

You may never have heard of CMV, even though the odds are good that

you are carrying it (up to 85 percent of adults over the age of forty do).

That's because CMV rarely causes a recognizable illness, even briefly:

about half of those undergoing CMV infection or reactivation suffer no

symptoms at all, while the other half are afflicted only with hard-to-

diagnose, nonspecific complaints such as general malaise, fever, and sweats.

But new research is showing us how CMV (and probably some other

viruses) can also cause serious long-term harm to those of us who only suf

fer mild and transient activation and reactivation of the virus. Because the

body can never quite consolidate its victory against these viruses, anti-

CMV memory cells get called up to active duty again and again, and over

successive iterations they gradually begin to ignore the apoptotic signal that

is supposed to scale back their forces at the cessation of hostilities. There

are various theories as to why this might happen, but I think it's most likely

to be part of a complex adaptation to protect us against uncontrolled cell

division (i.e., cancer) in these cells. 4 Whatever its origin, the inability to re

call these veteran troops progressively weakens the immune system's ability

to fight other infections, new or old. The iron limitations on the "immuno

logical space" or "military budget" ensure that, when the body can't cull

unneeded T cells specific to CMV or other infections, it has to make up the

numbers with other immunological soldiers. As a result, the numbers of

naive cells available to keep the body ready to face new threats, and of

memory cells for other pathogens, dwindle to dangerously low levels. 5

. . . They Just Fade Away

It's bad enough that death-resistant anti-CMV veterans refuse to take their

scheduled retirement, preventing needed redeployments and the hiring of

new recruits. But the situation is actually worse than this. These problem-


atic clonal expansions don't just refuse to make room for other soldiers to

do their job: like crippled or aged fighters, these weakened (the immunolo-

gist's term is anergic) T cells can't even carry out their own duties. 6

One of the most important factors crippling these anergic T cells ap

pears to be the loss of a key cell-surface receptor called CD28—an effect

that has been observed in humans 7 and animals. 8 T cells are alerted to the

presence of enemy forces by antigen-presenting cells (APCs), the immune

system's reconnaissance teams, which identify enemy combatants' antigens

through direct encounters with them or by digging through the rubble of

old battlegrounds (the remains of cells ravaged by them). When T cells lose

CD28, APCs can't recognize them to alert them to the danger, and their in

telligence report gets filed away unread. CMV-specific CD8 cells are un

usually susceptible to this loss.

Another problem with anergic CD8 cells is that, having staked out a

huge territory for themselves and thereby squeezed out other T-cell popula

tions, they simultaneously lose the ability to reproduce themselves. Memory

T cells normally express a receptor called KLRG1, which is there to keep

them from proliferating when no infection is present. But healthy cells bear

ing KLRG1 are able to reproduce when a threat is actually present. Usually.

Anergic CD8 cells have KLRG1 present on their surfaces,9 but they also

have another marker on their surfaces called CD57, which is lacking in nor

mal memory cells. 1 0 When CD57 is present at the same time as KLRG1, the

cells' ability to reproduce themselves is locked down tight, so that they still

can't transform their reserve division into a full-fledged army when their

sworn enemy is swarming over the ramparts.

Also contributing to this cellular "infertility" is the fact that the same

cells have short telomeres-—the long stretches of nonsense DNA that cap

our chromosomes' ends. Anergic T cells hit this problem because, unlike

most immune cells, they have lost the effective activity of the enzyme telom-

erase, which is required to renew telomeres. Most cells don't express telom-

erase, but it's essential to the healthy functioning of CD8 cells because they

are called upon to expand their numbers quickly and frequently over the

life span in response to new infections. So the lack of strong telomerase ac

tion is a further mechanism of the enfeeblement of these cells. See the side

bar, "Backgrounder on Telomeres and Telomerase," for more information,

which will be amplified in Chapter 12.


B A C K G R O U N D E R ON T E L O M E R E S AND T E L O M E R A S E

Every time a ceil divides, it must make a new copy of its DNA.

The enzyme responsible for doing this—called the DNA

polymerase—is a bit like a molecular monorail train, zipping for

ward along the "guide rail" provided by the DNA strand that it is to

replicate. As it travels along the "guide rail," the polymerase en

zyme makes a letter-by-letter copy of the strand beneath it, spool

ing the new, replicated strand out to the side as it goes.

DNA polymerase has a fundamental shortcoming, however.

For reasons whose details needn't concern us here, the machin

ery never quite manages to replicate the entire strand of DNA. A

small amount of a chromosome's DNA material is therefore lost

with every round of cell division, leaving the copied strand shorter

than the original. Eventually, the end of the chromosome is eaten

away.

A second problem that our cells have to solve regarding our

chromosomes is that they often break, due to radiation and other

stressors. The cell needs to repair such breaks. But what it must

scrupulously avoid doing is stitching two intact chromosomes to

gether end-to-end, mistaking the unjoined ends of the chromo

some for the unjoined ends of a broken chromosome. Thus, it

needs a way to recognize that the bona fide end of a chromo

some is not just one side of a chromosome break.

Telomeres are half of Nature's solution to both these prob

lems. Telomeres contain no genetic information—they are ex

tremely boring DNA consisting of many copies of a short

sequence—and they are present at the ends of all our chromo

somes. If this repeated sequence gets a bit shorter during succes

sive rounds of cell division and DNA copying, no harm is done until

it is mostly eroded. The other half of the solution is the enzyme

telomerase, which is able to add copies of that sequence to the

end of a DNA strand. This solves both problems: cells expressing

telomerase can compensate for the telomere shortening that oc

curs during cell division, and cells with or without active telom

erase can avoid stitching chromosomes end-to-end because the

P U T T I N G T H E Z O M B I E S T O R E S T 209

break-repairing machinery recognizes the distinctive telomeric se

quence and leaves it alone.

Humans and some other species have made ingenious use of

the telomere/telomerase system to protect themselves against

cancer. Cancer can only kill us by its cells dividing a lot; this is im

possible without telomerase, because without a way to renew the

telomere, it will slowly erode away, the chromosome ends will be

come indistinguishable from chromosome breaks, and the cancer

cell will be stopped in its tracks by a joining-together of some of its

chromosomes. Humans therefore turn off their telomerase genes

as thoroughly as they dare, so that a lot of mutation is needed to

turn telomerase on again and thereby allow a cancer to divide

often enough to kill us.

Although there's less research on it, old CMV carriers also suffer from

the expansion of defective CD4 cells—the "T-helper" cells that help other

immune cells to ramp up their counteroffensive when pathogens first in

vade. Outwardly healthy older carriers of CMV infection have the same

large clonal expansions of CMV-targeting but CD28-lacking CD4 cells as

are seen in their CD8 populations, leading to the same crowding-out of

other T-cell specialists and lack of responsiveness to activation by antigen-

presenting cells. 1 1

As with their CD8 cousins, CD4 cells stripped of CD28 can't respond

to antigen-presenting cells by deploying CD8 and other immune cells to

face the threat. Put this together with the inability of those very CD8 cells

to attack their targets effectively, and CMV would be left to run rampant,

generating yet more clonal expansions and wider immune dysfunction.

Clonally expanded anti-CMV CD8 cells are anergic (ineffectual) in

other ways, too. When they are first infected with their species' version of

CMV, young mice produce very effective CD8 cells targeting the virus,

which recognize at least twenty-four proteins specific to it; but after the in

fection becomes chronic, their anti-CMV forces become restricted to

clones that recognize an average of only five such proteins. 1 2 And older

CMV-infected humans' anergic CD8 cells mount a weaker response to the

threat than do younger infectees' cells, producing significantly lower

amounts of interferon gamma, a key chemical messenger responsible for

ramping up the T-cell response to the vi rus . 1 3 , 1 4


When Bad Generals Lead Good Armies

The failure of anergic T cells to clear out CMV infections then probably

leads to many of the other failures of immune function commonly seen in

the frail elderly that can't be chalked up to any direct effect of aging of the

cells in question. Some of these effects might be expected to flow from

changes in the production of cytokines by such cells, which influence the ac

tivity of many other soldiers in the adaptive and innate immune systems, but

others exert much more lasting changes than just problems in signaling.

Notably, it's now widely accepted that the aging of T cells is responsi

ble for the age-related losses in effectiveness seen in our B cells—the im

mune cells that produce antibodies to foreign antigens, which flag pathogens

for destruction by other cells. B cells rely on signals from CD4 (T-helper)

cells to mature and to develop antibodies, so it was only a matter of time

before someone confirmed that old T cells cause declines in the develop

ment and effectiveness of B cells, independent of the aging of the B cells

themselves. 1 5 , 1 6 , 1 7 Unfortunately, no one has (to my knowledge) yet directly

looked to see if these effects are due to the effects of CMV-inducell clonal

expansion that are so central to other aspects of T-cell aging, so we don't

know how much the specific phenomenon of anergic T cells contributes to

these declines. I'd be very interested in the results of such experiments.

Moving beyond the mechanistic studies and molecular biology, the real

impact of the creeping takeover of the immune system by anergic CD8

clones on the health of people bearing them is also becoming clear as sci

entists begin to study its influence. Animal studies show that age-related

clonal expansion of specific CD8 populations reduces the variety of T cells

present in their bodies and compromises their ability to mount an effective

immune defense. 1 8 The parallel in humans can be seen in findings such as a

poorer CD8 response to flu shots 1 9 and a blunting of the reinforcement of

T cell immunity to Epstein-Barr virus that can otherwise occur later in

life, 2 0 in people with clonal expansions of anti-CMV memory cells.

Taking the Full Toll

If the cost of anergic T-cell clones to the body were limited to the increase in

deaths and disabilities that can be directly chalked up to infectious disease,

that would be plenty enough reason to want to do something about them.


But there's considerable evidence that anergic CD8 cells contribute to age-

related morbidity and mortality from causes with no obvious immunological

link.

For starters, when you throw an influenza or influenza-induced pneu

monia attack onto an aged body, you wind up with shocking long-term

consequences that can greatly accelerate other disease process and hasten a

person's slide into helplessness and the grave. 2 1 A significant body of evi

dence shows that influenza in the elderly increases deaths from unexpected

sources like heart attacks, strokes, and seemingly unrelated respiratory dis

orders; it also worsens the course of congestive heart failure.

Also, the fact that it takes biologically old people so long to recover

from the flu, when overlaid on the general frailty induced by other aspects

of aging, probably contributes to serious, often permanent functional de

cay and disability. A bout of influenza often lays an older person in a hospi

tal bed for as much as three weeks, and studies show that for each day that

they spend "resting" this way, elderly people lose up to 5 percent of their

muscle power and 1 percent of their aerobic capacity. But no one thinks of

influenza or immunological aging when they see an elderly woman struggle

to open the doors at the mall, or slip on the ice and break her hip.

There are other age-related diseases in which anergic T-cell clones ap

pear to play an important role, but where the evidence is not nearly so

clear-cut. One is osteoporosis. Older women who have suffered an osteo

porotic fracture have been found to carry higher levels of anergic CD8 cells

than matched women with no bone disease, and there is a molecular basis

for thinking that defective CD8 cells are actually a cause, rather than an ef

fect, of the underlying thinning of the women's bones. 2 2

Additionally, albeit more speculatively, even the course of atherosclero

sis could be affected by the creeping "clonalisation" of the T-cell popula

tion, by leading to a state of chronic inflammation that could hasten a heart

attack. In support of this hypothesis, patients with coronary artery disease

have higher levels of anergic CD8 cells than otherwise matched healthy

people—a fact that is independently related both to CMV infection and

also to the presence of the disease itself.2 3 Thus, the weakening of the im

mune system appears to be both facilitating and also the result of arterial in

fections, which may in turn be the itchy trigger finger toying with the

loaded gun of atherosclerotic arteries.

As I said, the evidence for many of these downstream effects of anergic

T-cell clones is still not conclusive. But a couple of remarkable studies now


coordinated through the European Union T-CIA (T Cell Immunity and

Ageing) project have gone some way towards giving us a clearer picture of

the total cost, in deaths, of this driver of immunological aging, whatever

may ultimately wind up written on the death certificate.

These researchers hunted through two cohorts of Sweden's "oldest old"

(people in their eighties 2 4 and nineties, 2 5 , 2 6), selecting only people who were

particularly healthy compared to most people of their chronological age: free

of preexisting serious diseases of the heart, brain, liver, or kidney; without di

abetes or cancer or signs of existing, active infection or chemical markers of

inflammation; and not taking any drugs that have significant effects on the

immune system, including recent vaccination. The European team found

that even amongst these relatively healthy but old people, a few are silently

suffering a complex of immunological defects (the "immune risk pheno-

type") including several forms of aging damage that can be caused by CMV

infection—not least, the clonal expansions of anergic anti-CMV CD8 cells.

The facts that the resulting study population was healthy but very

calendar-old (by today's standards), and that some did and some did not

harbor anergic T-cell clones, allowed the T-CIA team to study their effects

"cleanly," in a population where its presence could really be said to predict,

rather than follow, preexisting disease, over the course of the next two years.

It was hardly a surprise that having the immune risk phenotype in

creased these people's chances of death—but the size of the effect was a

shock. The effect was especially powerful in the population in their

nineties, amongst whom its presence could predict 57 percent of the deaths.

This, remember, from the immunological aging damage induced by a virus

whose active infection state is passed through without any notice in many

people, and even in the rest of us usually causes only low-level malaise and

fevers.

It's important to see the full implications of this finding. The impact of

having the immune risk phenotype was seen at the level of all-cause mortal

ity, not just in risk of death from infectious disease. While pathogens do

claim many very biologically old people's lives, such deaths can't entirely

account for the result.

Slash-and-Burn for New Growth

As more and more evidence has accumulated fingering anti-CMV CD8 cell

clones in the age-related enfeebling of the immune system, immunologists


have begun to see the hopeful side of the phenomenon. If so much of the

aging of the immune system is indeed the result of this overreaching expan

sionism, then preventing or reversing it should (respectively) protect or re

store a youthful immune system in chronologically aged people. Vaccines

would again be as effective in people at presently advanced ages as they

were in their youth, and the enormous burden of suffering caused in the

old by infections that young people escape after an unpleasant day or two

home from work or school would be lifted.

One option for prevention, advocated by many immunologists, is vacci

nation against CMV. Even before we understood that CMV infection is a

central driver of the age-related weakening of the immune system, a 1999 re

port on the sluggish pace of development of new vaccines put out by the In

stitute of Medicine (IOM) of the National Academy of Sciences ranked the

pursuit of an effective anti-CMV vaccine as the highest priority item on the

list, based only on the then-known lifetime human and financial costs of

the virus. The U.S. National Vaccine Program Office would later agree, call

ing for more government dollars to go into CMV vaccine research. Today,

confronted with the strong evidence condemning CMV infection as a major

reason for the aging of the immune system, many immunologists are sound

ing the call for such investments even more loudly.

Though the merits of this case seem strong, it's worth noting that this

strategy is fundamentally preventative. While it can reduce the risk of CMV

infection, and possibly improve the immune response of existing infectees

to the virus, vaccination can't eliminate it—and it certainly can't reverse the

accumulated effects that a lifetime of CMV infection has had on the im

mune system. Thus, a CMV vaccine might save a relatively small number of

babies from suffering tragic birth defects, and prevent the deaths of many

AIDS and transplant patients, but it would do little for the many millions

of people already suffering with the chronic infections and continuous vul

nerability of having immune systems worn down by clonally expanded an

ergic CD8 cells.

Other proposals, which would at least have the potential to undo some

aspects of immunological aging, involve trying to remedy the defects of the

existing anergic T cells using gene therapy. The idea is that by delivering

copies of genes for proteins that are either missing or underactive in these

cells (such as those for the CD28 receptor or telomerase), we could restore

their effectiveness at doing their particular job, and prevent their suppres

sive effects on other T-cell populations. While there is some merit to these

proposals, there are also limits to their likely effectiveness and a lot of


uncertainties to their path to clinical development. And in the case of

telomerase, we'd still face the big worry that has to be taken seriously when

contemplating the introduction of telomerase into any cell, let alone one

that we know is wracked with aging damage: cancer. I'll talk about this

problem much more in Chapter 12, but here's a brief taster: because cells

require a minimum telomere length in order to keep reproducing them

selves, and because each cell division shaves off a little nub from the cell's

telomeres, cells with potentially carcinogenic mutations require a way to re

new their telomeres if they are going to go on to become full-blown malig

nancies. Nearly all cancer cells accomplish this by wrenching out the

self-imposed parking brake from their telomerase genes. Do we really want

to introduce this gene into defective cells—or worse, into "bystander" cells

in which telomerase should never be turned on, should some of the gene

therapy vector "infect" them too?

No: the solution here is not to try to rehabilitate these cells, but to get

rid of them. Older CMV infectees appear to have no shortage of functional

T cells targeting cells infected by the virus: it's just that these cells are sup

pressed by the crowding influence of huge populations of anergic ones.

And remember that even if we could restore all of these defective T cells to

their full immunological power, they would still cause problems so long as

they continue to sprawl out over precious, limited immunological real es

tate, preventing the retention of both naive and memory cells needed to

protect us from other pathogens.

The solution to this is conceptually simple. Remove the anergic T-cell

clones, and immunological space will be opened up for healthy cells of

other types and specificities to move in—and the repressive effects of the

anergic clones on their healthier anti-CMV cousins will be lifted.

The problem, of course, is how to purge anergic T cells from our sys

tems while leaving behind all (or, at least, nearly all) the healthy memory and

naive cells that we're trying to liberate from the former's repressive domina

tion. While oncologists can to some extent increase the effectiveness—and

decrease the toxicity—of drugs or radiation by applying them as narrowly as

possible to a relatively large lump at a fairly well-defined spot in the body, we

can't do the same against anergic T cells, which are spread all over the body

rather than being concentrated in one place. The same feature rules out sur

gery: tumors can often be removed (or at least beaten back) with the knife,

with varying degrees of safety and clinical benefit, but we will not be in a po

sition to pluck individual anergic T cells from the body one-by-one for the

foreseeable future.


But even though the cancer therapies of the recent past don't offer a

good model for the development of the required biotechnology, the most

exciting of the currently available and imminent treatments for cancer sug

gest a path to therapies that would indeed selectively eliminate the burden

of cells that will not die.

Smells like Gleevec

Even if no one you know has cancer, there's a good chance you've heard

about Gleevec (a.k.a. STI—571 or imatinib), Iressa (ZD1839 or gefitinib),

Herceptin (trastuzumab), and others less famous or still working their way

through the approval process. These so-called "targeted cancer therapies"

have been rightly hailed as breakthroughs; even the language of "miracles,"

although absurdly overused in popular books on health, seems justified to

many people who have seen tumors disappear from their own bodies or

from those of their loved ones, without the horrific side effects associated

with radiation and chemotherapy. Even so, these drugs are not completely

without side effects—no drug that "messes with metabolism" can be. Her

ceptin, for example, targets a growth receptor called HER-2: by tying up

HER-2, it prevents the excessive growth of cancer cells that get their

growth-stimulus fix by producing too much HER-2 on their surfaces. But

other, healthy cells rely on a low level of HER-2 stimulation to proliferate

normally. Because of this, Herceptin users can suffer deadly congestive

heart failure—a side effect that recent research has also uncovered in a

small number of users of Gleevec, which was thought to be an extremely

clean drug precisely because it only targets an abnormal form of a growth-

signal transducer. 2 7

In the same way, interfering with anergic T cells' resistance to apop

tosis might lead to their death, but this still leaves open the question of

how to undo this resistance without killing needed cells elsewhere in the

body.

I am confident that we can perform reverse-engineering, to adapt the

new targeted cancer therapies—and even newer ones that are now in vari

ous stages of clinical development—to develop the ability to create "smart

bombs" that will destroy anergic T cells (and also the other kinds of toxic

cells that we'll be discussing later on) with minimal harm to healthy ones. 2 8

We can foresee the ability to couple carefully chosen toxins to molecules

that home in selectively on the tell-tale signatures of anergic clones and


thereby to directly, decisively kill them flat out instead of just interfering

with their metabolism.

Light Kills Vampires

One cancer treatment that suggests ways to take out anergic T cells is photo-

dynamic therapy (PDT). PDT starts with a drug that, when illuminated with

laser light, either heats up greatly or produces a massive burst of free radicals.

Drugs exist that have this feature and are also taken up selectively by cancer

cells, allowing oncologists to cause a lot of photosensitizing drug to accumu

late in the target cells while avoiding much uptake by normal cells. By them

selves, PDT drugs are harmless, having no effects as long as the patient is

kept away from the light. Similarly, low-energy red laser lights is harmless to

people who have not received such drugs: the rays pass harmlessly through

the body. But when such a laser beam penetrates cells that contain a photo-

dynamic drug, the agent's photosensitizing properties are revealed in a sear

ing targeted blaze of heat or a maelstrom of free radicals that destroys the

tumor cells while leaving all but their very close neighbors unharmed.

The first PDT drug, Photofrin, was approved in industrialized coun

tries as a treatment for advanced lung, digestive tract, and urinary tract can

cers in the early 1990s, and more advanced versions are now in use

clinically or are in late stages of development. The most interesting of these,

Pc-4, accumulates more in some kinds of cancer cells than in healthy ones

because it dissolves well in fats, and these particular cancers have an un

usually high fat content. Once it enters the cell, certain features of Pc-4's

structure allow it to insert itself into the cancer cell's energy factories, the

mitochondria of which I've said so much in Chapters 5 and 6. Turn on the

laser, and the free radical bombardment begins, either taking the cell out

cleanly via radical-induced apoptosis, or at worst leaving some debris as the

cell dies the nasty way instead, when the free radicals tear through the cell,

cross-linking its proteins, turning its lipid membranes rancid, and wracking

its DNA with mutations.

The Molecular Swiss Army Knife

On the frontiers of medicine, we are now seeing the emergent use of nan-

otechnology—engineering performed at the molecular level—to destroy


cancer cells selectively, again providing us with a road map toward the devel

opment of a targeted therapy for toxic cells such as anergic T-cell clones. One

such technology is dendrimers: tiny particles with exquisitely complex

branching structures that extend outward like bushes, forming a spherical

shape (see Figure 2). Dendrimers' branches are engineered in a way that al

lows us to bind a wide range of molecules to them. This makes them like nan-

otechnological Swiss Army knives: several useful tools can be united into one

compact little package. Dendrimers can carry one molecule to target a given

cell type, one or more deadly drugs or other poisons to kill target cells once

they're located, and (if desired) a molecule that will allow researchers or doc

tors to track the progress of the whole package as it moves through the body.

One dendrimer under experimental development combines folic acid

(yes, the vitamin) with the established anti-cancer drug methotrexate and a

fluorescent compound called fluorescein. The folic acid is there to target the

dendrimer to cancer cells. Many cancers suck up massive amounts of this

vitamin because it is required for the production of new DNA—and be

cause the cell needs to create a whole new copy of its DNA blueprints every

time it divides, cancers have high metabolic requirements for folic acid to

support the feverish pace of their proliferation. To keep their reserves of

the vitamin topped up, many cancer cells "learn" to sprout veritable forests

of folic acid receptors on their surface.

Figure 2. An "unloaded" dendrimer.


Figure 3. Targeted dendrimer technology against cancer growth in mice. Redrawn. 2 9

This dendrimer was tested in mice that had been injected with a hu

man nasopharyngeal cancer line. Their tumors had grown quickly, reaching

a plateau at about fifty days. Giving one group of animals a low dose of

plain methotrexate had hardly any effect at all on the growth of the tumors

(see Figure 3). A dose more than four times as high (the "medium dose" in

the figure) reduced the growth rate quite significantly, but didn't actually

benefit the animals much: half of them were dead of either the tumors or

the side effects of the drug within thirty-nine days. Increasing the dose by a

further 50 percent (the "high" dose) brought cancer growth down to al

most nothing—but without doing the animals any good, because the drug's

toxicity caused the rapid loss of a third of the animals' body weight, and

again either allowed or caused the death of half of them just over a month

into the experiment.

But look at what was achieved with the same drug targeted using a

dendrimer! When targeted using this new technology, a dose of methotrex

ate equivalent to the lowest untargeted methotrexate dose was as effective

at slowing tumor growth as a dose of plain methotrexate over four times

higher. Moreover, the dendrimer-targeted methotrexate appeared to have

very low toxicity. 3 0

In a follow-up study, the same group compared the effects of the low-

dose methotrexate to those of the same dose delivered using the targeted

dendrimer, this time for an extended period of ninety-nine days. Left un

treated, the cancer-bearing mice began dying quickly—about fifty days

into the experiment—and low-dose methotrexate improved survival only


modestly. But by the end of the ninety-nine-day study, three out of eight of

the animals getting the dendrimer-targeted drug were still alive—and im

pressively, one of these animals was completely cured of its cancer by day

thirty-nine. Again, the dendrimer-targeted drug was nontoxic.

Switch the Hacksaw with the Toothpick

The beauty of dendrimers, like Swiss Army knives, is that they are so readily

customized. Researchers are experimenting with dendrimers bearing many

different targeting molecules and cancer-killing agents. One very clever ap

plication under development is a "dendrimerized" version of a one-two an

ticancer punch known as boron neutron capture therapy (BNCT)—a neat

idea that was first proposed over fifty years ago, but that until now no one

has ever quite managed to make work.

The idea behind BNCT is similar to photodynamic therapy. First, you

inject the patient with a form of the mineral boron. Once enough of the

mineral has accumulated in cancer cells, you flood them with low-energy

beams of neutrons. The boron itself is harmless, and so (more or less) is the

neutron beam. But when incoming neutrons hit the form of boron used in

BNCT, it absorbs them into its atomic nucleus and suddenly becomes ex

tremely unstable, releasing radioactive alpha particles. Alpha particles have

enough energy to nuke the cell in which the original boron is located and a

few of its neighbors, but they run out of energy quickly and the low-energy

leftovers are harmless. Thus, the boron-loaded cells are killed but no wide

spread damage ensues.

The trick, of course, is to find a way to target the boron selectively to

cancer cells, so that when you flip on the neutron beams you don't destroy

healthy brain and other tissue. Scientists have been trying to turn BNCT

into a viable clinical therapy for a rare, extremely aggressive, and hard-to-

treat brain cancer called glioblastoma multiforme since 1951, with some

limited success, but they've never achieved good enough responses to jus

tify using it as a standard treatment for the disease.

But scientists have recently reported very promising results in an ani

mal model of glioblastoma multiforme that was treated with a BNCT using

dendrimer-targeted boron. Human glioblastoma cells bearing a mutated

version of the epidermal growth factor receptor (EGFR) called EGFRvIII

that is implicated in the majority of these cancers were implanted into the

brains of rats. The researchers then heavily loaded their dendrimers with


boron, and then sent them hunting for the gliomas by attaching a mono

clonal antibody to the mutated EGFR. To get a handle on just how promis

ing the dendrimer really was, they compared its effects not only to what

happens in animals given no therapy at all, but also to animals given

p-boronophenylalanine (BPA—the most promising preparation of boron

being used in BNCT clinical trials), or else the boron-loaded dendrimer in

combination with (but not bound to) BPA. Within a day, about 60 percent

of the injected BPA-bearing dendrimer had homed in on tumors carrying

the mutant receptor, achieving concentrations that were about triple those

of BPA alone; the uptake by normal tissues was negligible. Impressed by its

homing ability, the researchers waited to see whether it could actually cure

the animals of their gliomas.

The results were decisive (see Figure 4). Untreated animals lived an av

erage of just twenty-six days. Animals who received BPA could expect to

survive for forty days: a significant improvement, but still a grim prognosis.

But animals given the dendrimer-targeted boron lived an average of seventy

days, with 10 percent of them surviving for six months—considered a

"cure" in the same way that five-year survival is considered a "cure" in hu

mans, since healthy rats have a life expectancy of about thirty months. And

animals that were lucky enough to get the dendrimer along with BPA sur

vived, on average, for a remarkable 85.5 days, more than three times the life

expectancy of the untreated animals, and more than double the survivor

ship of animals getting the best experimental therapy available. Plus, an im

pressive one in five of the BPA-plus-dendrimer-treated animals achieved a

"cure" as just defined.

Figure 4. Targeted dendrimer technology dramatically improves the effectiveness of BNCT. Redrawn. 3 1

Untreated

BPA neutron capture therapy

Dendrimer-targeted baron

Dendrimer-targeted boron plus BPA


Other targeting molecules, tumor types, and cancer-killing agents have

been successfully treated by dendrimers in experimental models. These

first-generation devices are turning out to be a very effective, versatile way

of creating specific, lethal missiles for seeking out tumors that express

known cell-surface receptors as hallmarks—and they offer promise for

anergic T cells, too.

PRO-Suicide Counseling

Today, gene therapy is a routine practice in mice, used to do everything

from testing experimental gene-based therapies, to investigating the effects

of turning genes on and off in an organism, to creating new models of hu

man disease by modifying animal cells to be more like human ones. Gene

therapy for humans is still highly experimental, but it's clearly only a matter

of time before we master it: the need for cures for congenital diseases, and

the potential utility of gene therapy in medical challenges as wide-ranging

as rheumatoid arthritis, trauma, dental tissue engineering and AIDS (to

name just a few), is providing the impetus for the basic and clinical science

needed to bring it into our therapeutic armory. 3 2

One option that gene therapy will furnish us with is the ability to build

a new suicide mechanism into our T cells that would cause them to self-

destruct should they ever turn anergic. Scientists have for some time been

able to introduce into mice (and other laboratory animals) genes that will

only turn on in the presence of a particular factor, such as an antibiotic, UV

light, a sugar, or even a signalling factor like calcium. This allows us to turn

such genes on and off at will, simply by administering the relevant factor.

The ability to introduce a gene that is only expressed when researchers

want it to be has been a powerful new tool for studying those genes' effects.

But these techniques are also now being turned to medical purposes. If, in

stead of designing these genes to be turned on in response to externally

supplied factors, we instead make their activation dependent on the pres

ence of a particular protein whose internal synthesis is diagnostic of a cell

that we want to be rid of, then we have yet another way to selectively target

cells for destruction.

Just as with the other targeting technologies I've discussed, the first

work in this direction has been in the cancer field. As I've noted, the one

absolute requirement for a cancer cell to threaten us is that it have a way to

keep renewing its telomeres: otherwise, its furious growth will grind to a


halt when it reaches the end of the telomeric line, which is long before it

can meaningfully threaten our health. Usually, this is accomplished by acti

vating the repressed gene for the telomerase enzyme—a gene that all of our

cells contain, but which is turned off in healthy cells most or all of the time.

So by "infecting" the cells of a patient with a "suicide gene" that would

be activated in the presence of high levels of telomerase, cancer cells could

be killed from within. This would eliminate the need to target a drug or the

immune system to the offending cell: every cell would hold within it the

seeds of its own destruction should it ever turn to the dark side.

In principle, we could generate a literal "suicide gene" that would de

stroy the cell in the presence of the tell-tale protein. Indeed, this has already

been done in animal models of cancer, using genes that regulate apopto

sis; 3 3 anergic T cells are resistant to apoptotic signaling, but this resistance

might be overcome by bombarding them with insistent messages to shrivel

and die. But there's an even better alternative that's under more advanced

development. This uses the somewhat more readily controlled—and there

fore safer—technique of installing the gene for a protein that is largely

harmless in itself, but which activates an inactive form of a deadly drug—a

so-called "prodrug."

Prodrugs are substances that are inactive and harmless until they are

metabolized in some way, whereupon they are chemically transformed into

a pharmacologically active product. Most prodrugs are activated by en

zymes in our livers and are then released in active form to the rest of the

body, but others act more like molecular "sleeper agents," going about the

body unobtrusively, minding their own business and blending in with their

environment, until a prearranged signal is given—and their hidden pur

pose suddenly becomes revealed in the form of a precision strike on their

target.

Several antiviral drugs, such as the herpes drug ganciclovir (Cytovene/

Cymevene), work somewhat along these lines. Ganciclovir stops viruses

from using the DNA-replication machinery of their host cells to reproduce

themselves. It does this by interfering with the action of the virus's unusual

version of thymidine kinase (TK), an enzyme that is required for the syn

thesis of DNA.

Thymidine kinase's job is to make thymine (a "letter" in the DNA

code's "alphabet") available to be added onto the new DNA chain, by join

ing thymidine to phosphate molecules taken from the "energy currency

molecule" ATP. Ganciclovir acts like a molecular impersonator on a mission

to sabotage an enemy factory. It first uses its strong structural resemblance


to thymidine to fool the viral TK into thinking that it is that molecule.

Duped, TK hands over thymidine's rightful phosphate group to the drug.

Ganciclovir then uses its shiny new phosphate group to perpetuate its

identity theft, presenting its phony credentials to the cell's DNA synthesis

machinery, which unknowingly inserts it into the emerging DNA strand in

thymine's place. At this point, the sabotage of the hijacked equipment is

accomplished, because while the machinery can slide ganciclovir onto the

DNA strand, it can't add any further genetic letters onto ganciclovir once

it's in place. Without the ability to copy its DNA, the virus can't replicate

itself, and its expansion campaign is brought to an abrupt end; all that's left

is for the immune system to besiege and ultimately destroy the cells in

which the remaining virus is holed up.

If ganciclovir were as good at tricking the version of the TK enzyme

used by our own cells as it is against the viral version, it would potentially

be a very effective cancer-killer: again, cancer can only survive by keeping

up the insane pace of its growth, and turning this off by shutting down its

DNA synthesis capacity quickly tames tumors. But, of course, such a

drug would come with some pretty serious side effects, because it would

shut down the growth of normal cells at the same time. This might make

it an acceptable therapeutic bargain for cancer—the effect would wear

off after the drug was withdrawn, allowing patients to recover—but it

would make it totally unacceptable for its present use as a herpes treat

ment.

In fact, however, ganciclovir is rather poor at mimicking the human TK

enzyme, and its effects are thus mostly restricted to turning off virus

replication—though it does have some negative impact on the body's abil

ity to regenerate its blood cells and on the production of sperm. But a team

of Japanese and American scientists recently realized that they could in

principle use the viral TK/ganciclovir combination to shut down cancers if

they could introduce the enzyme into cancer victims' cells using gene ther

apy, but turn it on exclusively in cancer cells.

As I've already indicated, there is one obvious way to distinguish can

cer cells from normal ones which could provide a mechanism for control

ling the activation of viral TK: active telomerase. By designing a version of

the viral TK gene that would be attached to a "trigger" (promoter ) that

would turn the gene on only in the presence of telomerase, the researchers

realized that they could set the enzyme to work in a cancer patient's malig

nant cells, while leaving it dormant almost everywhere else in the body.

At this point the flow chart of what they were designing was beginning


to look like the biotech equivalent of one of those exceedingly convoluted,

multistep devices that players build up in the board game "Mousetrap."

The scientists would set the "trap" by first seeding a copy of the gene for

the viral TK enzyme, complete with its special telomerase "trigger," into

every cell in the patient's body. The patient would then swallow some gan

ciclovir tablets, which would penetrate all of his or her cells indiscrimi

nately.

In most cells, the drug would have no effect, because nearly all cells

have their telomerase enzyme firmly turned off. But when ganciclovir en

tered a cancer cell, the trap would be sprung. The cancer's abundant telom

erase enzyme would flip on the viral TK enzyme; the TK would scoop up

the ganciclovir, adding on the phosphate group needed by DNA "letters"

for insertion into the emerging DNA copy strand; the next time it reached

for the relevant "letter," the DNA-copying machinery would grab the

phosphorylated ganciclovir by mistake, jamming it into the "letter's" place

on the strand. At that point, you would almost hear the cry of "Mousetrap!"

as the DNA synthesis machines seized up, cell division came to a screech

ing halt, and the cancer shut down. See Figure 5.

Figure 5. How ganciclovir enables viral thymidine kinase to kill mammalian cancer cells.


It was a crazy, convoluted solution—but it worked in the test-tube

against liver, kidney, pancreas, and thyroid cancer cells. Moreover, the

setup proved largely harmless to normal rat thyroid and human skin cells. 3 4

So the team took the next step in bringing something off a lab bench and

into a clinic: a careful study in laboratory animals.

The researchers first cooked up two batches of customized viral TK

genes: one with the telomerase-activated "on" switch, and another with a

switch that could be expected to be flipped in healthy and cancerous cells

alike. They then slid these genes into viruses from the same family as the

common cold, allowing them to literally infect animals with the gene con

structs. They first tried these constructs out on healthy animals, to see what

the potential was for side effects. As expected, animals that got viral TK un

der the control of the nonselective promoter suffered nasty liver damage

upon injection with ganciclovir, while putting in the same gene under a

telomerase promoter appeared to be basically harmless, since there were no

telomerase-expressing cancer cells present to activate it.

At this point, the researchers decided that their experimental therapy

was ready to hit the next stage: a test in animals that had been injected with

implanted human thyroid carcinoma cells. Giving such animals a copy of

the viral TK driven by a promoter that did not rely on the presence of

telomerase to activate it brought tumor growth to a complete standstill—

but, as expected, it also prevented normal cells from reproducing them

selves, leading to nasty liver damage.

But when scientists tried the selective targeting of viral TK to cancer cells

by using the telomerase promoter, ganciclovir shut down tumor growth just

as completely as it had when the TK was controlled by the nonselective

promoter—and without the latter's toxic effects. The apparent safety of this

highly selective intervention is all the more convincing when you remember

that the effect can be turned on and off at will, by administering or with

drawing the ganciclovir.

Know Your Enemy

We've seen that biologists can be just as creative as weapons engineers

holed up in the Skunk Works at finding new ways to target and kill cancer

cells selectively, i.e., leaving healthy cells unharmed. It is foreseeable that

the same methods in use or under development against cancer could be

used to target anergic T cells. In this case, we're blessed with an enemy that


is walking around with a bull's-eye painted right on its chest. The same dys

functional receptor profile that strips anergic T cells of their ability to recog

nize their target antigens (absence of CD28) and to proliferate in response

to infection (presence of KLRG1 and CD57), possibly along with some

other markers (such as reduced levels of CD154, implicated in the failure of

old T cells to support B cell development) already allows scientists to iden

tify these cells, and could also be used to target such cells for destruction.

Unleashing the wrath of the immune system against its oppressors would

be poetic justice, but vaccination (either passive or active) against these cells

might be tricky. For one thing, their most prominent antigenic feature is the

lack of a cell-surface protein (CD28), and while we could target the combina

tion of KLRG1 and CD57, it's not yet clear whether all unwanted cells ex

press these two proteins, nor whether other, desirable cells do. As it happens,

immunologists already do identify anergic cells using a combination of im

mune proteins—but these could not easily be used for vaccination purposes.

Also, after all, the problem that we're looking to resolve is characterized by a

poor response to vaccination, so an "anergic T-cell shot" might only be effec

tive in relatively immunologically "young" people. So while this approach is

promising for many kinds of toxic cells, it may be less so for CD8s.

But that still leaves us with a lot of options. Dendrimer-based targeting

approaches seem the most straightforward, because they allow for the tar

geting of cells via multiple identification criteria, and also because they can

introduce any number of poisons into the cells that they select, from out

right toxins to boron for BNCT.

And while using vaccines to target anergic T cells might be problematic,

there could be another way to use the immune system as a proxy army, coop

erating with it to restore the sovereignty of the immune system's government-

in-exile. Remember that anergic CD8 cells first become a problem because

they stop listening to the apoptotic order to scale back their forces that's sent

out after their target pathogen has been routed from the body's frontiers.

They are able to ignore these orders because they produce high levels of bcl-

2, a protein that blocks apoptotic signalling.

This suggests the possibility of restoring normal apoptotic signaling in

such cells by delivering "antisense RNA" for bcl-2's blueprints to them-—

strips of genetic material matched to the transcribed DNA instructions for

the protein, preventing the encoded bcl-2 from actually being produced in

the cell. With bcl-2 production brought down to normal or nearly nonex

istent levels, anergic CD8 cells would finally hear their curtain call and

bow out.


Would purging the immunological "space" of anergic T cells be

enough to rejuvenate the immune system completely? I can't say for sure,

because it hasn't been done—and, as I am well aware, the body is an in

credibly complex machine whose parts have not yet all been identified, let

alone their purposes and interactions. Existing research tells us pretty

clearly that the direct and indirect immunosuppressive effects of these cells

are powerful enough that a thorough spring cleaning of them will pro

foundly improve T cell-mediated immunity, and also very probably the

functioning of other aspects of the immune system that T cells support and

govern. But we'll only know just how profoundly once we've done it.

I can tell you right now that there is at least one aspect of immune aging

that the removal of anergic T cell clones will not address: thymic involution.

The thymus is a gland located just behind your breastbone. It's where im

mune cells first produced in your bone marrow go to learn to become T

cells. As we age, the thymus loses cells and shrinks away, and in the process

its output of naive T cells plummets. This, of course, imposes further limits

on the body's ability to respond to new threats.

In principle, there is a fairly straightforward way of dealing with this,

however: stem cell therapy. This is foreseeable biotechnology, as we will see

in the next chapter (see the sidebar there, titled "Rebuilding the Thy

mus"). 3 5 The accomplishment of such a goal would entail significant ad

vances in the stem cell field, including mastering the art of turning

embryonic stem cells into the progenitors of the different cells of the body,

and then engineering new tissue to rejuvenate the old one, renewing old tis

sues with pristine new cells—but these are just the same problems that are

being solved quite rapidly for tissues all over the body, so there is ample

reason for optimism.

That's all I have to say about the immune zombies; now it's time to look

at some other types of supernumerary cells.

Deadly Combat in the Battle of the Bulge

The second kind of toxic cell that we'll want to rid ourselves of is excess fat

tissue—most important, the so-called visceral fat that surrounds your inter

nal organs, as opposed to the subcutaneous fat that lies under your skin all

over the body. It's widely believed that, as people get older, they just "natu

rally" become more resistant to the effects of the hormone insulin, whose

job it is to move carbohydrates and amino acids into fat and muscle cells.


This change causes a range of threatening metabolic changes, the most ex

treme of which manifest in people with full-blown type II ("adult onset")

diabetes. It's also common wisdom that older people "naturally" enter into

a more inflammatory state, with the body slowly burning up from within

because of an excessive production of inflammatory signal molecules.

When you take in more calories than you expend, your body hangs on

to them rather than allowing them to go to waste. This is not the result of

perversity on the part of evolution, but a survival strategy: until very re

cently (by evolutionary standards) there was a good chance that quite soon

you'd be in a period of famine, when those stored calories would be your

lifeline. If your body isn't under the kinds of challenges (like weight-

bearing exercise) that signal the body to build up metabolically expensive

muscle or bone tissue, it will take the easy way out by storing the calories as

fat. But in an environment where feast is never followed by famine, and

where exercise is almost entirely a voluntary affair, we fail to shed that extra

fat tissue, and it slowly accumulates as we age. Because this accumulation is

a difference of aging versus healthy young bodies, it qualifies as "aging

damage" under my engineering definition, even though it might not be

considered as such from a purely theoretical point of view.

It's long been known that this damage—in the form of being over

weight or obese—puts you at greater risk of diabetes, heart disease, and

various other ailments, but it's only recently become clear why and how.

You may have heard that fat stored in different parts of the body has differ

ent health implications: having an "apple shape" (fat centralized in your

midsection, as in a "beer belly") puts you at great risk for diabetes and

heart disease, while having a "pear shape" (fat clumped on your bottom or

thighs) is unsightly but much less hazardous to your health. To the extent

that there is some biomedical basis for this distinction, it lies in the differ

ence in the locations of visceral and subcutaneous fat. Visceral fat is most

visible around your middle because it clumps around major internal organs

like the liver and kidneys. By contrast, subcutaneous fat just lies under your

skin—and of course, there's skin all over your body, though there are more

prominent depots for this fat type in some places than others.

Recent studies have found that nearly all observed age-related insulin

resistance, and much of the age-related pro-inflammatory signaling shift,

can be attributed to the accumulation of excess visceral fat, which precedes

and predicts the development of all the elements of the metabolic storm

known as syndrome X: insulin resistance, low HDL ("good") cholesterol,

and high blood pressure, triglycerides (blood fats), and blood sugar.


Even more tellingly, when you compare people of different ages, you find

that the difference in insulin effectiveness between young and old disappears

when you account for the difference in fat, and visceral fat in particular. 3 6 , 3 7

In striking studies at the Albert Einstein College of Medicine, aging an

imals have had most of their resistance to insulin and other hormones re

versed by highly invasive surgery that scrapes out most of their visceral fat,

making their body compositions similar to much younger animals, or to an

imals of the same age that had been subjected to calorie restriction (among

whose benefits are dramatic reductions in age-related insulin resistance and

inflammatory signaling). 3 8 This latter result was especially striking because,

when the scientists looked at the distribution of fat in the calorie-restricted

animals, they found that they actually had more subcutaneous fat than their

young counterparts, but less visceral fat—and their insulin effectiveness

was almost the same.

Further pinning the blame on visceral fat, a recent study confirmed

that undergoing liposuction—whose invasiveness and risks of trauma are

kept low by removing only the relatively easy-to-access but cosmetically sig

nificant subcutaneous fat, while leaving the much harder-to-remove vis

ceral fat behind—does not improve the insulin resistance associated with

the original obesity. 3 9 On the other side of the same coin, several studies

have now shown that putting overweight people on low-calorie diets or ex

ercise programs significantly improves their insulin resistance quite early

on—well before it has had a chance to impact their overall weight by much,

but after it has had time to reduce their level of visceral fat, which (fortu

nately) is the first thing to go when energy needs aren't being met.

The reasons for all of this have become clear as scientists have increas

ingly come to understand the nature of fat itself. Fat tissue was once con

sidered to be just inert storage space, like carrying around a spare tank of

gas on your derriere. Instead, we now know that it is a metabolically active,

dynamic tissue that secretes and responds to a range of hormonal and other

signaling molecules. We also now appreciate that fatty tissue is not com

posed only of "fat cells" (ad ipocy tes) , but is a mixture of different cell types,

including supporting connective tissue, nerves, and blood vessels, as well as

immune cells—notably, macrophages. In fact, adipocytes are actually derived

from the same precursors as macrophages, and secrete many of the same

immune-system regulating molecules, such as the coagulation-enhancing en

zyme plasminogen activator inhibitor-1, and pro-inflammatory signaling

molecules (cytokines) such as tumor necrosis factor alpha, monocyte

chemoattractant protein-1, and interleukin-6.


As the size of the fat depot increases, adipocytes begin pumping out

more and more of these inflammatory molecules, some of which promote

infiltration of the tissue by macrophages and some of which signal the pre

cursor cells that give rise to both adipocytes and macrophages to take the

path toward the latter instead of the former. Macrophages, in turn, produce

even more inflammatory messenger-molecules, creating a self-reinforcing

inflammatory feedback loop.

The most exciting finding in the emerging science of fat in the last ten

years has been the discovery that these signaling molecules not only cause a

potentially pathological increase in systemic inflammation, but also in

crease the body's resistance to insulin. This conclusion is supported by

studies showing that isolated muscle and fat cells become insulin-resistant

when bombarded with the very inflammatory mediators that adipocytes

and macrophages produce, and that chubby lab rodents' insulin resistance

is relieved by aspirin treatment, in part via blocking the effect of cytokines.

And the relationship doesn't just hold up under the artificial conditions of

the laboratory: during sepsis (the inflammatory storm generated in response

to severe infection), human patients often exhibit very severe insulin resis

tance as part of the immune response.

Evidently, these and related questions will keep an army of basic and

clinical researchers in the diabetes field busy for decades, resolving para

doxes, isolating deeply intertwined metabolic pathways, and double-

checking their results in different models. But for engineering purposes,

fortunately, we don't have to wait to have the results of these investigations:

we just need to observe the presence of damage, and fix it.

Doing It the Old-fashioned Way

In this case, of course, there are two very simple, inexpensive solutions that

don't involve advanced biotechnology: diet and exercise. But unfortunately,

as decades of research and centuries of anecdotal experience have shown,

most of us find it very difficult to lose weight once we put it on. As little as

a 100-calorie daily energy imbalance—about what you get in a single

medium-sized biscuit—accounts for the standard weight gain that creeps

up on the average person in the decades between high school and middle

age, and while it's easy to load it on, it's hard for most people to shed those

extra pounds and keep them off. The situation is not nearly as dire as is of

ten made out—studies show that about one overweight person in five


successfully achieves long-term weight loss, and research is clarifying what

it takes to get there—but the metabolic consequences of excess visceral fat

are far too deadly, and the magnitude of the current obesity epidemic far

too staggering, to leave the cure of this form of aging damage to self-help

programs or public health measures designed to remediate our present

"toxic food environment." 4 0 Realistically, unless we are ready to leave the

fate of millions to a sudden wave of greater personal or political responsi

bility, we must look for biomedical solutions to visceral fat.

Fat for the Fire

One option that we might pursue is to shrink away visceral fat by causing it

to burn off its excess stored energy. Scientists have of course been trying to

develop drugs to do this for decades, but so far the only moderately effec

tive such drugs are amphetamines, and their side effects and addictiveness

clearly don't fit our remit.

For several years, the appetite-regulating hormone leptin seemed to of

fer the chance of shrinking fat and maintaining insulin sensitivity. An ex

tremely rare genetic mutation that leads to a congenital lack of leptin makes

both rodent and human victims monstrously obese, and injecting these

mice with leptin leads to dramatic weight loss. Causing these rodents to

produce more leptin inside their fat cells (using genetic engineering) makes

them eat 30 percent to 50 percent less food, leading to more insulin sensi

tivity and an almost complete disappearance of their body fat. Moreover,

the effects are stronger than can be accounted for by their newfound light

dining habits alone. 4 1 Fat cells of animals with the extra leptin gene were

expressing other genes that activate mitochondria, turning them into little

"fat burning machines." 4 2 Paradoxically, however, while injections of leptin

lead to rapid fat loss in both normal and obese rodents, the same level of

leptin that would peel away the pounds in lighter mice circulates naturally

in the bodies of their fat cousins, necessitating a much higher level of leptin

to achieve similar weight loss. This is in part because leptin is, ironically,

produced by the very fat cells whose swelling with stored energy it was sup

posed to inhibit, so that chubbier rodents naturally produce more leptin,

not less. And indeed, after drugs giant Hoffmann-La Roche invested a for

tune to develop a way to mass-produce human leptin in genetically modi

fied bacteria, they found the hormone to be a miserable failure as a

weight-loss treatment. 4 3


This led scientists to speculate that overweight members of both

species come to suffer "leptin resistance" in the same way that they suffer

insulin resistance: levels of the hormone are high, but cells stop responding

properly to its signals to turn off the appetite and turn on fat-burning. Re

cent studies by Roger Unger, the researcher who had originally raised

hopes for leptin by showing its powerful effects in mice, show how this can

happen at the molecular level. When you overfeed mice a high-fat, high-

calorie chow, their fat cells scale back the expression of the genes that tell

the cell how to build leptin receptor "doors" on their surfaces, so that the

cell stops hearing the signal. 4 4 Similarly, unpublished studies of the fat tis

sue of grossly overweight people show that their expression of the leptin

receptor gene is consistently so low as to be undetectable, while lean, young

people may have anywhere from quite low to extremely high levels of gene

expression at any given time. 4 5

Unfortunately, as with leptin itself, the path to using leptin receptor

gene therapy as a way to reverse the negative effects of visceral fat is not a

clear one. Mice with the extra leptin gene may have stayed slim in the face

of an overly rich diet, but they did not fully escape its consequences: they

still suffered the same "ectopic" (mislocalized) fat infiltration of their livers,

muscle, and heart as did mice lacking the extra leptin receptors eating the

same chow, and their insulin resistance—the key negative effect of excess

visceral fat that we need to address—was just as bad.

While we might find some way of avoiding some of this by turning the

gene on and off again, thereby restoring our insulin sensitivity, it seems un

clear how we would deal with the ectopic fat. We might expect that as soon

as we turned the gene off the calorie imbalance that had led to the initial

overgrowth of fat cells would begin again; while we would shrink fat cells

back down with each round of therapy, we would have no way to eliminate

the cells themselves, and over the course of a greatly extended life a visceral

cavity full of large numbers of even relatively small fat cells might still lead

to metabolic mayhem.

Really Tr imming the Fat

No—what seems most likely to solve the problem of visceral fat is not to try

to tame it, but to cull it: actually to remove a substantial number of the

bloated, excess cells. The same sorts of cell-specific targeting of cancer or

anergic T cells we've been discussing seem likely to be applicable to visceral


fat too; and while, unlike in those other cases, no specific markers of vis

ceral fat cells have been identified, we don't need to be nearly so specific.

Unlike cancer or anergic T cells, some fat—including some visceral fat—is

not only metabolically harmless, it's necessary for carrying on the business

of life. Aside from being a spare tank of metabolic fuel that we draw upon

and refill every day, those metabolic factors we've been talking about—

energy-regulating hormones, inflammatory peptides, and others—also have

healthful uses. As with all of metabolism, this was built into us by evolution

for our benefit. As anti-aging engineers, it's not our job to interfere with

it—just to prevent the damage that it causes in aging bodies.

Night of the Living Dead

The last class of toxic cells that I want to address in this chapter are so-called

"senescent" cells. 4 6 They got this name because of the (rather dubious) anal

ogy drawn between these cells and aging humans by their codiscoverer, Dr.

Leonard Hayflick, then of the Wistar Institute in Philadelphia. These cells,

like the others that we've been discussing, begin their lives as normal con

stituents of the skin, joints, and other tissues. They are normally quiescent,

not dividing regularly, but they remain capable of reproducing themselves

on demand, as part of their normal function (unlike "postmitotic" cells,

which lose the ability to divide ever again once they reach their mature form

and are only r ep l aced by new cells coming from the body's stem cell pools—

if they're r ep l aced at all).

The defining feature of senescent cells is that they, like postmitotic

cells, have lost the ability to divide. Hayflick observed, contrary to the

dogma of the day, that cells from these tissues would not keep reproducing

in the petri dish indefinitely: they would seem normal for several successive

periods of replication, but would then suddenly enter into a twilight state

in which they didn't die, but became in various ways abnormal. Their ap

pearance became blotchy, their shapes irregular. They failed to form the

neatly whorled colonies of mutually adhering cells that were the norm in

younger cultures. And above all, they stopped reproducing themselves.

The use of the word "senescent" to describe these cells is, however, a

bit misleading. When people hear about these cells, they often assume that

cellular "senescence" is the ultimate fate of all of the cells in the body with

age, and that the entry of "young" cells into this senescent state is the un

derlying cause of aging. Moreover, the term evokes an image of these cells


as somnambulant old has-beens, sleepwalking through the remaining days

of the rest of the body's life, not contributing anything to the organs in

which they reside but also not doing us any positive harm. Their only

downside, we might think, is a crime of omission: inability to replenish ag

ing organs.

In fact, senescent cells are generally held to be extremely rare even in

very aged people. 4 7 However, their possible role in aging has turned out to

be far more complex—and far more active—than we at first imagined.

The most obvious characteristic of senescent cells is, as mentioned, their

loss of the ability to reproduce. But, like worn-out lechers, senescent cells

desperately try to stimulate themselves into activity—pumping out sub

stances that, though essential to their healthy function back when they were

contributing members of a healthy tissue, may promote the development of

cancer when present in excess. Various mechanisms are involved.

For a start, some of the most common signal molecules overproduced

by senescent cells are chemical messengers like epidermal growth factor that

directly spur cell division in their neighbors.

As a second example, many senescent cells also overproduce protein-

digesting enzymes such as matrix metalloproteinases (MMPs), which are

the "demolition teams" of tissue remodelling. These enzymes perform the

essential function of clearing away the old, damaged "scaffolding" in which

cells are embedded in a tissue, making space for new growth. But, just as

having the outside wall of your house knocked down during a renovation

would leave you vulnerable to burglary, so an excessive or uncontrolled

MMP activity can enable cancerous cells to escape from the restraints of

the tissue in which they were originally embedded, and/or to work their

way into new tissues far removed from the original cancer site—the metas

tasis process.

And most recently, scientists have found yet another way that senescent

cells potentially roll out the welcome mat for nascent cancers: by churning

out dangerous overdoses of vascular endothelial growth factor (VEGF) 4 8

and stromal cell-derived factor 1 (SDF1), 4 9 which promote the growth of

new blood vessels.

As you can see, the picture turns out to be a lot more complicated than

we had once thought. As I'll discuss later on, the senescence phenomenon

is probably an evolved response to DNA damage, helping to prevent that

damage from becoming cancerous. From the point of view of that one cell,

this is an extremely effective short-term protection against cancer, because

it shuts down the cell proliferation that is the very heart of the disease. But


it seems likely that the "unlifestyle" that a senescent cell leads ultimately fa

cilitates cancer progression in the long term by destabilising its neighbors.

So—you guessed it—they've got to go.

Putting the Zombies to Rest

One way to eliminate senescent cells is to make them no longer senescent. In

cell culture experiments, this has been achieved in a variety of ways, such as

by relengthening exhausted telomeres with telomerase or by depleting pro

teins associated with senescence. But reversing senescence would run the

risk of cancer, because senescent cells typically get that way as a response to

potentially carcinogenic changes to the cell, such as damaged DNA, hyper

active cancer-promoting genes, or (again) very short telomeres, which pro

mote a mutagenic state. Restoring proliferative capacity in such cells could

potentially take us out of the frying pan of senescence and into the fire of

cancer.

Similarly, approaches based on turning off the dangerous metabolic

abnormalities of senescent cells carry risks, because other, healthy cells de

pend upon these same pathways for normal function. Chronically jamming

growth signals, enzymes, and inflammatory messengers might well prevent

senescent cells from watering the seeds of cancer, but it would also lead to

"crop failures" of cells all across the body.

As usual, the engineering approach to this dilemma is to rewrite the

rulebook. We will maintain the body's evolved capacity to shut down cells

in danger of going cancerous, by leaving the metabolic regulation of senes

cence as it is. Indeed, as we'll see in Chapter 12, we will ultimately need to

transform the body in ways that will make it almost immune from cancer by

ensuring that all cells run out of steam long before they would threaten us

with uncontrolled cell growth. But we will eliminate the threat posed by

those cells that do senesce by eliminating the cells themselves.

Silver Bullets

The first significant development in this area came in 1995, in a lab at the

Lawrence Berkeley National Laboratory headed by Dr. Judith Campisi,

one of my coauthors on the original SENS scientific manifesto. Campisi

and coworkers found that a relatively easy, reliable test for the activity of an


enzyme called senescence-associated beta-galactosidase (SA-beta-gal) could

identify senescent cells not only in petri dishes, but in skin samples taken

from older humans.

Unfortunately, SA-beta-gal is not a perfectly selective marker for senes

cence. As subsequent studies showed, the enzyme does occur in nonsenes-

cent cells—usually at very low levels, but sometimes in high concentration.

It turns out that, contrary to the simple interpretation of the Campisi lab's

findings, this enzyme is actually identical to one that is normally found in all

of our lysosomes—the cellular waste incinerators, whose clogging (you'll

recall from Chapter 7) underlies many of the worst pathologies of aging.

The change into the senescent state does not suddenly trigger the secretion

of SA-beta-gal into the main body of the cell out of nowhere: instead, it ap

pears that there is always some low level of SA-beta-gal floating around in

even normal cells, as can be detected with techniques that assess the level of

the enzyme itself in the cell—but the level is so low that its activity is barely

(if at all) detectable by the methods that Campisi's lab initially used, which

are unfavorable to the enzyme's functioning. 5 0 , 5 1 , 5 2

But as a cell goes through round after round of replication—thereby

drawing ever closer to senescence—its SA-beta-gal levels rise. 5 3 Probably

this is because the cell begins to overproduce the enzyme in response to the

stresses of aging—notably, the need for more lysosomes as they become less

and less effective at doing their job (and also as their cell division rate,

hence garbage dilution rate, slows and the job thereby becomes intrinsically

more challenging). Eventually the level gets so high that its activity is no

ticeable even under suboptimal conditions.

SA-beta-gal activity is, notably, found at abnormally high levels in cells

taken from tissues where cells are under stress, due to inflammatory dis

eases that fuel cell proliferation (such as chronic hepatitis C, atherosclerotic

plaques, and venous ulcers). Most interesting is the finding that levels of the

enzyme shoot up in cells undergoing "cr is is ," 5 4 , 5 5 a period in which cells

that have somehow escaped senescence are still undergoing cell division

and the erosion of their telomeres. Such cells usually just run out of steam,

but occasionally they undergo a mutation that removes the clamp from

their telomerase genes, making full transformation into malignancy almost

inevitable.

What's emerging, then, is a picture of SA-beta-gal as an enzyme that

appears at high level in the main bodies of cells undergoing some kind of

stress that may ultimately threaten their neighbors. This might mean that

by using high levels of SA-beta-gal as an identifier for the destruction of


senescent cells, we would simultaneously take out some useful "targets of

opportunity."

However, we may be able to establish a system of double-checks, to

help us weed out more genuinely senescent cells while leaving more inno

cent (but suspicious-looking) cells unmolested. This is because, in addition

to SA-beta-gal, senescent cells also produce abnormally high levels of other

molecules involved in the programmed senescence response. Senescent ba

boon skin cells, for example, contain an activated form of the protein ATM

kinase, which responds to DNA damage by activating several tumor sup

pressor genes, including the famous p53. Senescent cells also exhibit high

levels of p53, as well as the binding protein (53BP1) by which its gene in

teracts with ATM kinase, and p21, a senescence regulator that works under

p53's command. 5 6 Some senescent cells also contain high levels of p l 6 , the

other main regulator of the process. Levels of this protein, for reasons as

yet unknown, also climb slowly with age in nonsenescent cells, making it an

unreliable marker for senescence when taken in isolation; but it—like these

other features—could still potentially be used as part of a double-checking

mechanism, with multiple proteins being used to distinguish genuinely

senescent cells from those expressing only one of them for unrelated rea

sons. 5 7

This chapter has focused on the accumulation of toxic cells with age,

and the foreseeable biotechnology with which we should be able to purge

ourselves of those cells as part of our platform for the rejuvenation of our

bodies—restoring the immune system, alleviating metabolic mayhem, and

protecting our cells from being goaded on to cancer. In the next chapter,

I'll look at the opposite problem: cell loss with age, and the scientific—and,

just as importantly, political—hurdles that we face in bringing forward the

ability to renew our tissues with fresh, new replacements.

11

N e w C e l l s fo r O l d

Throughout our lives, we gradually lose cells vital to our

continuing health. Many fatal diseases of aging—such as

Parkinson's disease—are caused by the loss of populations of

cells responsible for one or another crucial function in the body.

Fortunately, therapies based upon stem cell research offer the

possibility of recreating our missing cells, good as new; politics

stands in our way as much as any remaining scientific obstacles.

After the enormous effort that had been required to organize the

conference, it was an incredibly rewarding moment to see the man who was

revolutionizing stem cell biology take the podium in front of a packed

crowd of colleagues.

It was the second conference I'd run at Cambridge focusing on scientific

progress toward the reversal of human aging, so the pressure was on for me

to top the success of the first. I'm on the board of the International Associa

tion for Biomedical Gerontology (IABG)—one of the few biogerontological

societies in the world with an explicit brief to pursue the development of bio

medical solutions to aging—and a couple of years earlier I had volunteered to

spearhead their tenth conference. I knew at the time what I was getting into.

The society would provide little logistical assistance beyond networking op

portunities, so I would have little help beyond the support (moral and other

wise) of my beloved wife Adelaide, and that suited me perfectly. With the

formal authority of a society already on the progressive wing of the biogeron-

N E W C E L L S F O R O L D 2 3 9

tology community, I wanted to push the envelope a little further, and being

left to my own devices meant that I would not have to debate my priorities

with a committee.

Despite the society's mandate, previous IABG conferences had tended

to be dominated by the same kind of presentations that I saw at every

biogerontology conference I attended (and I try to get to most of them): ba

sic science, geriatric medicine, and work in model organisms that the re

searchers hoped might someday be translated into a pill to slow down aging

in humans. I took on the enormous and exhausting work of running this

conference because it would give me the opportunity to highlight work that

could contribute to a panel of interventions designed to reverse aging.

IABG 10—the meeting that would be, in retrospect, the first in a series

of SENS conferences—was an enormous success. I am saying so myself, but

I am making no boast of my own: the enthusiasm with which my colleagues

thanked me for my efforts at the end of the week was ubiquitous and unmis-

takeably genuine. Attendees were surprised and excited by what they had

heard, not only on its own merits but because most of it was completely

novel to them. This was to be expected: while a typical biogerontology con

ference invites a roster of speakers almost entirely drawn from within the

biogerontological community, I had introduced a strong interdisciplinary el

ement, bringing in researchers working in cancer, diabetes, stem cells, and

other fields, whose work would in my mind be critical to the development of

effective anti-aging biomedicine but who were almost entirely unknown to

researchers prone to pegging themselves in the "biogerontology" slot.

At the same time, those presenters had the opportunity to mix with re

searchers in whose laboratories the degenerative processes of aging were, if

not being reversed, certainly being dramatically delayed in mice and other

model organisms. This was work that often hardly raised an eyebrow

amongst biogerontologists, who were immersed in a field in which it had

been taking place since the first calorie restriction experiments nearly seven

decades previously, but which amazed the experimental oncologists and tis

sue engineers that I had brought in to show the biogerontologists what

they'd been missing.

IABG 10 was so successful in meeting my academic goals, and the re

quests from my colleagues that I run a sequel were so obviously sincere, that

I felt sure that I could harness its momentum to make it the de facto inaugu

ral meeting of an ongoing series of academic conferences on SENS science

at Cambridge. From then on, however, I knew that the effort would be en

tirely my own: I could not rely on the support (nor brook the interference,


little though it had been) of the IABG or any other society. Challenging as

the job of directing such events was, I knew it would be worth it.

On the other hand, I also knew that I had set my own bar quite high

with the first conference, and that some of my colleagues would be less in

clined to attend a conference not run under the aegis of a recognized

biogerontological society. This was all the more so when I was the organiz

er, because a whispering campaign against my credentials as a scientist had

been initiated by some of my genuinely well-intentioned but old-school

gerontological rivals shortly after the first conference. So if I wanted to get

people to show up to SENS2, and to have the series continue, the quality of

the conference lineup would have to be top-notch despite the opposition. I

would have to meet an ambitious standard—and I wanted to overachieve.

The Master Cells: Accept No Substitutes

I knew that I would once again want to devote a whole session to embryonic

stem cells (ESCs)—the primordial "master cells" from which our mature

cells spring, and which play a critical role in our development into complex

multicellular organisms from the simple ball of cells that is an early embryo.

Thanks to the tragic confusion of the science of ESCs with the ethical, le

gal, and religious disputes around the status of the embryo in the abortion

debate, ESCs are the one plank of the SENS platform with which you can

not help but be familiar. You have doubtless heard that, with the right kind

of biochemical stimulation, embryonic stem cells can be coaxed into be

coming any kind of cell in the body: nerve, muscle, heart, kidney, the lot.

These resulting, "differentiated" cells can then be used to repair or to

replace cells and tissues that are lost to—and whose loss is a central patho

logical feature of—multiple debilitating, often nearly untreatable diseases,

including many of the worst scourges of aging. ESCs will be needed to de

velop full cures for Parkinson's disease, spinal cord injuries, juvenile dia

betes, amyotrophic lateral sclerosis ("Lou Gehrig's disease"), heart attack

damage, some cancers, and other devastating conditions—including aging

itself. Indeed, under the purely pragmatic, engineering definition of aging

that clarifies so much about what needs to be done to keep our bodies age

less indefinitely, the net loss of cells is itself a form of aging damage. This

makes it a central target of SENS.

However, because media coverage of the issue focuses on the political

firestorm rather than on the real, hopeful medical story of ESCs' enormous


potential as medicine, you may still not be clear on the key differences in

basic biology and therapeutic potential between ESCs and adult stem cells.

There are also important differences between ESCs derived from embryos

being stored in fertility clinics and those that can be custom-made for each

patient out of his or her own mature cells by fusing them with egg cells (a

technique known as somatic cell nuclear transfer, SCNT, to which we shall

return). For this reason, I will spend a little time disentangling these issues.

True ESCs are found only in very early-stage embryos called blasto

cysts, which are the very primitive balls of cells that are formed within just a

few days after sperm meets egg. The embryo only remains in this stage of

development very briefly; it has developed much further by the time the

embryo is implanted in the womb. It is from the blastocyst that every cell in

the mature organism must be derived, yet the blastocyst itself has none of

these differentiated cells: no neurons, no heart cells, no insulin-producing

beta-cells, and so on. So for the embryo to go on to transform itself into an

organism with the complex structure of a human being, its cells need the

ability to transform themselves into each and every one of those mature

cells—a power called pluripotency.

Adult stem cells, on the other hand, are much more limited in their abil

ities, and also with good reason. These cells emerge in the late stages of de

velopment, and are retained in particular tissues during life as a reserve to

replenish cell stores. They thus hold on to only the limited repertoire of

possible fates that is relevant to their role in that particular tissue. Thus,

blood stem cells can become oxygen-carrying red blood cells or any of the

many blood-borne immune system cells, but (despite what has been

claimed—see later on in this chapter) they cannot form either neurons or

heart muscle cells: if asked, a blood stem cell would doubtless indignantly

reply, "That's not my job." They're there to fulfill a specific role in the body,

and to do it well, but not to be on reserve to heal all damage everywhere.

This more limited range of developmental flexibility (or "plasticity") is

called mul t ipo tency . 1

Indeed, there are many areas of the body for which there are no adult

stem cells dedicated for use in repair—and, as you might expect, these in

clude the areas that suffer the worst cell loss during aging. This is the situa

tion, for instance, in much of the brain. For many years, it was believed that

the entire brain loses cells over the course of normal aging, and that there

was no way for the body to replace these losses. This dogma was overturned

a few years ago, largely due to the work of Fred Gage and his coworkers at

the Salk Institute, who showed that the brain does indeed harbor stem cells


capable of renewing some parts of the brain. This has led to a swing, in the

popular imagination, to the impression that the entire brain has the inbuilt

capacity, through its adult stem cells, to keep the entire brain young and

functional.

In fact, however, that impression is also wrong. Only a small number of

areas in the brain produce stem cells capable of developing into new neu

rons: a sub-subsection of the hippocampus called the subgranular zone of

the dentate gyrus, and a part of the subventricular zone, where neurons are

created to supply the olfactory bulb (the area of the brain that processes the

sense of smell). There's evidence that some of these cells do attempt to re

pair areas of the brain damaged by age-related disease, but there's little ev

idence that they're much help. After a stroke, for instance, a few of the stem

cells formed in the subgranular zone do change their normal habits and mi

grate toward the site of damage, but over 80 percent of them die within a

few weeks, and the remaining cells replace only about 0.2 percent of the

cells destroyed by the incident. 2

Why do we maintain the capacity to replace neurons in some areas of

the brain and not others, like the cerebral cortex where our long-term

memories are stored, or the frontal lobe where our ability to make and stick

to plans for our future is centered? Most likely, it's because the olfactory

bulb and the dentate gyrus are the only places where evolution has encoun

tered the need for a regular influx of new cells within the brain's "biological

warranty period." Both those areas have short-term functions that require

the regular renewal of their cell populations. There is no built-in popula

tion of adult stem cells to deal with cell loss induced by the ravages of aging

and age-related neurological diseases such as Alzheimer's and Parkinson's.

As you'll have realized if you still remember Chapter 3, this is because,

while these disorders have their seeds in molecular damage that occurs

throughout life, that damage does not reach a threshold where function is

impaired sufficiently to affect Darwinian fitness in a short, Paleolithic hu

man lifespan.

Another example of a tissue in which cells die but are not naturally replaced is the thymus, a key organ in the immune system which acts to "ma

ture" precursor cells into T cells. Its regeneration using stem cells is at an

early stage of development, so there's not much to tell you yet, but a proof

of concept exists in a rare but very serious congenital disease—see the side

bar "Rebuilding the Thymus." I've described the immune system generally,

and T cells in particular, at some length in Chapter 10, so you might want

to refer back to that chapter while reading the sidebar.


R E B U I L D I N G THE T H Y M U S

The promise of using stem cells to treat thymic involution can

be seen in recent advances in treating babies with DiGeorge

syndrome—a genetic disorder whose victims are born with a vari

ety of defects, including having a thymus gland that is underdevel

oped, or in some cases completely absent (the latter being called

"complete DiGeorge"). Complete DiGeorge has, until recently, of

ten been a very near-term death sentence: with no ability to pro

duce T cells, these babies would die of infections that are trivial to

the rest of us, within a few months of leaving their mothers' wombs.

The obvious way to solve the problem of a missing thymus is

transplantation, but that's a tricky business: to do its job, the tissue

needs a very good blood supply and plenty of oxygen saturation,

which is difficult to achieve without the natural penetration of tiny

blood vessels. There have also long been problems with rejection

and graft-versus-host disease: perversely, sometimes a few of the

child's bone marrow cells will "spontaneously" transform into dys-

regulated T cells that don't recognize either the child's own anti

gens or the thymus tissue donor's. This leads to a ferocious attack

on both, usually killing the child; moreover, often the donor's T cells

would turn on the transplant recipient's foreign tissues in an

equally deadly, reciprocal attack.

Recently, surgeons and immunologists at Duke University de

veloped a protocol using very thin slices of tissue to ensure maxi

mum transfer of oxygen, which are engrafted into the child's thigh

to give it a generous, readily accessed supply of blood, along with

a novel immune-suppressing drug that targets T cells specifically.

The intervention is still experimental, but it's become progressively

better through new innovations and now seems relatively success

ful. In a 2004 report, the Duke team found that five of the six pa

tients receiving the new therapy were still alive fifteen to thirty

months later, a greatly improved survival rate.

If, instead of using transplants of foreign tissue, we could take

the child's own stem cells, coax them into becoming thymus cells,

and engraft them, we would eliminate the need for risky immune

suppression. Then, if we could encourage these cells to grow in a


scaffold in which we could build up a complex organ structure, in

cluding a proper blood supply, we could abandon the highly un

satisfactory replacement of an organ with a wafer-thin tissue slice

in favor of a real organ "transplant." We may never actually be

able to do this in DiGeorge syndrome, for the simple reason that

we don't have enough time—but if a foreign tissue implant can

generate viable T cells and increase survival in babies born with

no thymus, then I can only see promise in delivering a person's

own cells, taught to become T cells and if necessary coaxed and

structured into a more complex tissue, to an existing but atrophied

organ, to restore it to youthful functionality,

Similarly, in the heart, cells exist, which some researchers have called

"cardiac progenitor cells" or similar names; but, while these cells can be

nudged into showing some stem-cell-like molecular signatures in a test

tube, they have not been shown to form heart cells in the body. Indeed,

some closely related stem cells found elsewhere in the body (mesenchymal

stem cells) have the same hallmarks but definitely cannot become heart

cells. Whatever the ultimate truth of the matter, what we do know is that

neither these nor any other cells in the body step in to heal the massive

damage wrought to the heart muscle by being starved of oxygen during a

heart attack—as any cardiologist or heart-attack survivor can sadly attest.

Again, the reason for this lies in the cold statistical analyzes effectively per

formed by natural selection after generations of genetic dice-rolling in a

premodern environment: heart attacks don't kill twentysomethings, so by

evolution's calculus it's not worth investing in a repair system that will al

most never be used before its owner is killed by something else.

In the first days of the political debate around embryonic stem cells,

some very respected laboratories issued reports of ESC-like flexibility in

adult stem cells—of blood-forming cells spontaneously transmuting them

selves into liver and brain cells, and perhaps most promisingly of such cells

being injected into the hearts of rats given simulated heart attacks, forming

new heart muscle tissue, and restoring functionality to the organ. These re

ports were taken so seriously that several groups began early clinical trials

in humans, in which stem cells have been derived from the bone marrow of

heart attack victims and then injected into their ravaged cardiac tissue.

But independent laboratories have been unable to confirm these


claims. Instead, what may be happening is that the cells are indeed being

incorporated into the tissues in question, but are doing so by fusing with

the existing c e l l s . 3 , 4 , 5 , 6 , 7 , 8 , 9 , 1 0 There may be some limited benefit to this: the

process of fusion may support the surviving cells in damaged tissues, either

by secreting growth factors needed during repair, or by helping new blood

vessels to grow into the tissue. 1 1 But, while such effects may help to keep a

disintegrating ticker beating for a short while more, it cannot substitute for

actually rebuilding heart tissue, either for heart attack victims or for the

aged humans whose hearts we wish to rejuvenate.

Indeed, recently the New England Journal of Medicine published the

results of the first trials of bone marrow stem cells as a treatment for human

heart attack victims that were large enough to give meaningful information

about actual clinical outcomes in the patients (as opposed to just collecting

safety data and early reports of physician and patient experience). One of

these trials 1 2 found no benefit, and the other two 1 3 , 1 4 reported what the

Journals summarizing editorial described as "small, [statistically] signifi

cant, but clinically uncertain improvements" 1 5 in treated patients com

pared to those receiving dummy injections. They reported no evidence

either way on the subject of the cells actually transforming into heart mus

cle cells, but the animal studies mentioned above have at this point dashed

previous hopes of such an effect.

Contrast these weak effects with the results of an animal study using em

bryonic stem cells to treat an induced heart attack. Eighteen sheep were sub

jected to such an assault, and then allowed to decline for two weeks. During

this time, scientists harvested ESCs and nudged them to begin making the

transition into becoming heart muscle stem cells. Before the embryonic stem

cells had completed their developmental journey, the researchers seeded

these cells onto the hearts of half of the group, while for comparison the re

maining nine animals were left to slide further down the road to disability.

Where the benefits of adult stem cells had been dubious, the healing

influence of ESCs was undeniable (see Figure l a ) . The cells took hold in

the damaged hearts and were shown to transform into mature heart cells,

and the animals exper ienced a dramatic recovery. In the two weeks since

their matched relations had been given the ESC treatment, the control

group's hearts had lost an additional tenth of their blood-pumping ability.

By contrast, animals who had received the cardiac-committed stem cells

enjoyed a 6.6 percent improvement in pumping capacity.

And if you dig into the details of the study, you find even more reason

to be optimistic about the potential for ESCs as a therapy for the heart. For


2 weeks after

infarction, but

before

transplantation

Controls ESC-transplanted

Figure la. Restoration of the heart's pumping ability by embryonic stem cells, (a) Controls vs. ESC recipients, (b) Controls, ESCs plus immunosuppressive drugs, and ESCs alone. Redrawn. 1 6

one thing, the scientists in this study waited until two weeks after the ani

mals suffered their heart attack to do anything about the damage to their

hearts, and it was during this period that the bulk of the degeneration of

the animals' hearts' pumping capacity occurred. Early intervention,

whether with stem cells or even with more conventional medical duty-of-

care, might have prevented a lot of this decline, potentially leading to much

better outcomes after ESC treatment.

Second, the ESCs that were used in this study weren't even derived

from sheep, but from mice—an important point to which we will return

later. While the cells clearly did their job—maturing into heart cells, unit-

1 month

after cell

transplantation

2 weeks after

infarction, but

before

transplantation

1 month

after cell

transplantation


ing with the native tissue, and restoring significant functionality to the ani

mals' hearts—it still seems reasonable to think that using cells that were ac

tually from their own species would have yielded a better metabolic and

functional match, and, therefore, better outcomes.

And third, the average improvement in the ESC-treated group actually

conceals a very positive variation in response to ESCs within the group. Be

cause of the possibility that their immune systems might reject the mouse-

derived ESCs and spoil the experiment, five out of the nine treated animals

had been given immune-suppressing drugs. It turned out that the drugs

were unnecessary: the researchers took slices from all animals' hearts after

the study was over, and there was no evidence of inflammation or attack by

immune cells in the hearts of the animals given ESCs, no matter whether

they were dosed with immunosuppressive drugs or not.

This is positive news in and of itself, but there was even better news to

follow. The reported 6.6 percent recovery of heart pumping capacity in

ESC-treated animals was a pooled result, including animals that did and

did not receive immunosuppressive drugs. When the researchers broke

down the results according to whether animals received these drugs or not,

they found that the immunosuppressed animals had actually responded

more weakly to ESC treatment than ones whose immune systems were left

to carry out their business. The sheep in the ESC-only group healed 25 per

cent more scar tissue from their original heart attacks than the drug-treated

animals, and their hearts recovered over twice as much pumping capacity:

about a 9 percent versus roughly a 4 percent gain (compared, again, to a 9.9

percent further loss of functionality in animals not receiving ESCs—see

Figure lb ) . So, in evaluating the prospects for human use of ESCs, we

should look at the stronger results available from an ESC-only approach,

rather than the weaker results from pooling these animals together with

those given immunosuppressants.

After this study was published, the first head-to-head comparison of

ESC versus adult stem cell therapy for heart damage similar to that en

dured during a heart attack were reported; the results showed clearly the

superiority of the ESCs, which transformed into heart muscle cells, achieved

long-term incorporation into the animals' heart tissue, and improved the

animals' heart function, while the bone marrow stem cells had no signifi

cant effect.17

And this is only the beginning of the biomedical promise of these

amazingly versatile cells. Embryonic stem cells have been used to cure ani

mal models of some of the most fearsome diseases human beings suffer,


Controls ESC + Immune- ESC Alone Suppressing Drug

Figure lb.

such as juvenile diabetes, 1 8 spinal cord injuries, 1 9 , 2 0 multiple sclerosis

(MS) , 2 1 cerebral palsy, 2 2 stroke, 2 3 , 2 4 Parkinson's disease, 2 5 a form of paraly

sis caused by a virus that induces a standard mouse model of ALS, 2 6 and—

very recently—macular degeneration (the form of blindness caused by the

loss of light-sensing cells in the center of the eye's retina). 2 7 All of these are

diseases where a person's native, adult stem cell supply fails even to begin

to replace the cell loss caused by the disease.

Of course, none of these therapies has made its way into the clinic—

yet. But there's every reason to think that they will lead to dramatic im

provements in our ability to treat these patients. The balance of preliminary

evidence from human trials using fetal cells or cells derived from stem-cell

tumors (not true ESCs) in Parkinson's disease and stroke victims, for in

stance, already shows a lot of promise that can only be expected to improve


with the use of actual stem cells, and recently a study using ESCs in a mon

key model of Parkinson's has confirmed their ability to transform into the

required type of neurons, engraft into the appropriate area of the brain,

and relieve many of the symptoms of the disease. 2 8 These are exciting times.

Why We Need Them

Because the horizons for the ultimate fate of ESCs as differentiated cell

types are wide open, and because of their ability to proliferate indefinitely

(unlike adult stem cells, whose replication capacity tends to be more lim

ited), the scientific consensus acknowledges the greater therapeutic poten

tial of ESCs over that of adult stem cells. There are certainly therapeutic

uses for adult stem cells; indeed, the only stem cell-based therapies currently

in clinical practice are things like bone marrow transplants, which use adult

stem cells taken from a donor or from the patient's own body. But the oft-

repeated claims by social-conservative lobby groups that adult stem cells

can effectively treat "70 diseases" or "more than 65 diseases" have rightly

been called "patently false" and the accompanying information on one

prominent such group's Web site "pure hokum" in the editorial mentioned

earlier from the normally diplomatic New England Journal of Medicine.

As things stand, only embryonic stem cells hold the potential—both in

terms of the range of cells required, and in terms of the sheer quantity of

cells needed to create large tissue grafts and in some cases even whole

organs—that will be needed to make young bodies from old ones. And

need them we will. In addition to cells lost to heart attacks and neurode

generative diseases, the truth is that we are losing cells—and the function

ality that those cells provide—from our tissues on a continuous basis.

Parkinson's disease, for example, is the result of the loss of neurons in the

brain that produce dopamine, a chemical messenger involved in fine con

trol of the muscles. You get a clinical diagnosis when you have lost about

half of these neurons, impairing this control enough that parts of your body

begin an involuntary rhythmic shaking and your face turns into a staring

mask with a fixed blank or even hostile expression. But all of us are losing

dopamine-producing neurons every day to aging; people with Parkinson's

just lose them more rapidly, reaching the clinical threshold earlier. Without

the ability to replace these cells, we'll all develop the disease eventually (if,

as the refrain goes, something else doesn't kill us first).

And it's happening all over your body, and not just for the kind of in-


trinsic metabolic reasons that are most precisely termed "aging." You are

permanently losing cells every day to molecular damage caused by the re

active by-products of normal metabolism, and even after we undo such

damage using the foreseeable biotechnologies of the SENS platform, we

will still need to reverse these losses if we are to build ageless humans. Plus,

we also lose cells to other causes. We all regularly destroy some naturally ir

replaceable cells to minor bumps on the head, moments of oxygen depriva

tion, and the apoptosis ("programmed cell death") imposed on cells by the

body when it senses that they are doing more harm than good.

Whether these latter cell losses are a part of "aging" is debatable, but

fortunately it's not an issue that we need to resolve in order to get moving

on the restoration of old and dysfunctional bodies to the full health and

functionality of youth. Replacing these missing cells will play an essential

role in anti-aging biomedicine, no matter what the causes of their attrition

or their relationship to "aging" in the abstract. Progressive cell loss repre

sents a change away from the healthy ideal of youth, and therefore an anti-

aging engineer should work toward fixing it, just as any engineer will work

to restore machinery back to the state in which it functions best.

Throwing Away the Key to the Medicine Chest

Adult humans have adult stem cells, not embryonic ones: again, true ESCs

only exist in blastocysts. Thus, getting a supply of ESCs for use as cellular

medicine involves somehow deriving such cells from early-stage embryos.

Fortunately, there is a quite generous—and heretofore almost untapped—

supply of such cells that is already being produced by an existing industry:

in vitro fertilization (IVF) in fertility clinics.

The chances of any given IVF embryo being successfully implanted

and then carried to term as a result of the procedure are still relatively low,

so fertility clinics routinely create several embryos from the sperm and eggs

supplied by either would-be parents or their donors. That way, they have a

supply of embryos available for multiple attempts, without requiring

women to undergo multiple rounds of the expensive, very unpleasant, and

modestly dangerous hormonal treatments required to extract eggs from

them. Typically eight such embryos are left over after every round of IVF,

with the result that there were 400,000 surplus embryos frozen in storage in

American fertility clinics alone as of 2002. At least 16,000 of these are

unclaimed by any donor, an additional 45,000 have a similarly murky sta-


tus, 2 9 and nearly none of the others will ever actually be used in fertility

procedures. These embryos are ultimately discarded, or become sufficiently

decayed that they cease to have any potential to form a baby.

This is what makes the debate around the use of embryos from fertility

clinics such a frustration to doctors and scientists. These embryos are

slated for destruction no matter what we do with them: there is no chance

that the vast majority of them will ever be implanted in a womb and un

dergo the additional development needed to make a baby. The opponents

of ESC research and therapy have proposed preventing their disposal by

implantation into volunteers who would carry them to term for adoption,

but even in that scenario there is no realistic prospect that even one percent

of such embryos would be diverted from the rubbish tip. Once created, the

fate of those blastocysts that are not actually implanted into a woman is

sealed; the only question is whether scientists will be allowed to use their

cells for research and as cures.

Actually, the insertion of these cells into the midst of the abortion debate

is even more artificial than this makes it sound. Blastocysts are so primitive a

stage in embryonic development that they have not yet made the biochemical

"decision" to become a distinct human being. This is part of why they have

the full flexibility to become any type of cell in the human body—and also

why the confusion of stem cell technology with the abortion debate is so eth

ically misguided. At this early stage, for instance, an embryo could still divide

into two separate cell populations, each of which can go on to become a sep

arate, unique person. Indeed, this is exactly what happens when identical

twins are formed. Since this ball of cells can still go on to become either one,

or two, or even more different people, clearly the unified cell mass that pre

cedes this separation does not embody the identity, the essence, or the soul of

any single, personal human being. And while we can stand in justified awe of

the potential for life (or lives) locked up in these cells, that should not cloud

our ethical vision into thinking of this potential as morally being even in the

same ballpark as the actual lives of patients that need its cells for medicine,

when it is closest to that of skin cells in a petri dish.

The Nicodemus Solution

Powerful though embryonic stem cells derived from embryos left over from

IVF may be, however, they do have one potential disadvantage hanging

over their medical use. Cells derived from such embryos will, by definition,


be immunologically alien to the patient's own cells, making them a target

for attack by the immune system. Thus, the same kinds of problems that

currently plague conventional organ transplantation—the horrors of rejec

tion, graft-versus-host disease, and the dangers of living with an immune

system turned off artificially with drugs to preserve the transplant—might

possibly be an issue in embryonic stem cell transplants, too.

So far, the evidence suggests that we will be able to manage this issue

with little hassle in many cases. Much of our confidence on this front de

rives from recent experience in actually using ESCs in experimental treat

ments for various diseases. Most such studies have just assumed that

rejection would be a problem, and have preemptively taken steps to pre

vent it, either by using animals with defective immune systems, or by ad

ministering immunosuppressive drugs. But more recently, some studies

have been performed using ESCs without taking such steps, and the results

suggest that there may have been nothing to worry about in at least some

cases. In the sheep heart-attack study I mentioned earlier and in several ro

dent s tudies, 3 0 , 3 1 ESCs taken even from another species have incorporated

themselves into the "patient's" native tissues and provided substantial re

generative benefits, with no rejection issues.

Such results may mean that ESCs' state of development is so early and

tentative that they may not even distinguish themselves with enough anti

gens to create a problem across the species barrier—let alone the barrier

between individual humans. Additionally, it now appears that ESCs pro

duce their own, very localized immunosuppressive signalling molecules

that selectively protect them from immune attack, and even trigger any at

tacking killer T cells to undergo self-destruction (apoptosis). 3 2 Because

these mechanisms involve either direct cell-to-cell contact or factors se

creted and used very close to the stem cells themselves, this local immune

shielding system is free from the systemwide side effects of taking immuno

suppressive drugs.

Moreover, in some specific applications the risk of rejection will be low

to begin with, because the tissues where we'll be delivering the cells are

substantially shielded from the immune system. A lot of the nervous sys

tem, for instance, is largely inaccessible to immune attack (which is how the

virus that causes shingles can hide out there for years after being purged

from the rest of the body).

We can also lower the risk of rejection by providing patients with ESCs

from isolates ("lines") that are a match for all of the major antigens

involved, which we could readily do in many cases if we are allowed to pick


and choose our stem cell lines from among the embryos currently slated for

destruction. It has been calculated that a bank of just 150 donor embryos

randomly selected from the existing stockpile could do this perfectly for

one patient in five, provide a probably usable match for almost two in five,

and allow for a long-shot match for almost 85 percent of potential patients—

and if we were able to choose specific immunological combinations out of

the surplus instead of choosing embryos at random, just ten such donations

could give grade-A matches for nearly 40 percent of patients and good

matches for over two-thirds. 3 3

But we can't yet rule out the possibility that rejection may present a

barrier to our effective use of ESCs in human medicine for aging and dis

ease. In that case, the good news is that technology exists that already al

lows us to generate embryonic stem cells that are a perfect immunological

match for animals as complex as cattle and monkeys, and several scientific

teams say they're on the verge of being able to do the same thing for hu

mans. I've already mentioned it: somatic cell nuclear transfer (SCNT). In

SCNT, doctors begin by taking a mature cell from the patient's body (a "so

matic cell"), by for example swabbing the inside of the cheek, and then turn

hack its clock, releasing it from the strictures of a mature, differentiated

complexity and transforming it into a patient-specific embryonic stem cell.

This biological miracle is accomplished by a technique that is incredi

bly simple. The metamorphosis occurs in an egg cell, provided by a donor.

This cell's nucleus is removed to make way for the one from the patient's

cell. With a biochemical boost or a zap of electricity, the two become one,

and the egg begins dividing just as it would if it had been fertilized, kick-

starting the production of embryonic stem cells created from a patient's

own genetic instructions, creating a perfect immunological match (see Fig

ure 2). The cells can then be used for medicine just as any ESC would be,

but with absolutely no fear of rejection.

Actually, you may well already have heard of this advanced biomedical

research under a name more popular with the media: therapeutic cloning.

While this term is perfectly scientifically accurate, it has generated an enor

mous amount of confusion about the nature and purpose of SCNT, splash

ing political napalm onto the heated fires burning in legislatures and online

chat rooms surrounding stem cells. Let me try to extinguish those flames.

To a scientist, the word "clone" means simply a set of genes, cells, or or

ganisms that are identical to one another at the DNA level because they are

derived from a single ancestor. We've used the word in this strict scientific

sense in the "clonal expansion" of T cells, and the "monoclonal antibodies"


Figure 2. How SCNT ("therapeutic cloning") works.

that are currently used to treat some cancers and will probably be used as

part of our panel of engineering solutions to aging. Similar uses of the word

occur when scientists speak of a "clone" of common bacteria bearing a

gene that turns them into tiny biological factories for the production of in

sulin for diabetics, or even when gardeners talk about a "clone" of strawberry

plants.

But say "clones" to even highly educated people who don't work in a

few disciplines of biology and biomedicine, and you evoke images of a sea

of indistinguishable, zombielike drones, enslaved to technocrats or created

for other sinister purposes. That this confusion is corrupting the debate

about this potentially essential life-saving technique can be seen starkly in a

speech delivered to the Canadian Parliament on February 27, 2003, during

debates surrounding Canadian legislation to regulate stem cell research.

Mr. James Lunney, a Conservative party member of Parliament for the

Nanaimo-Alberni riding on Vancouver Island, began by saying that "[I]f

we took one of [the speaker of Parliament's] cells, extracted the nucleus

and put it into an ovum, one could stimulate it electrically and allow it to

grow." So far, so good. But then Mr. Lunney rocketed off into a grotesque

but all-too-common flight of misunderstanding: "The so-called therapeutic

clone would be to take the immature model of Mr. Speaker and extract an

organ, if he needed one, killing the clone in the process. That is so-called

somatic nuclear cell transfer or therapeutic cloning." Similar outrageous


confusions have been perpetrated on the floors of the U.S. Congress and

elsewhere in the course of the stem cell debate.

SCNT doesn't involve making clones of people at all. It involves mak

ing blastocysts—balls of cells that, as we've seen, have not yet even made

the necessary steps to decide whether they will become one, two, or more

people. True, these blastocysts could in principle be used to make babies if

they were implanted into a woman the same way as is done with blastocysts

produced through IVF, but this is a potential, not a fact. When blastocysts

are created by SCNT for therapeutic purposes, no egg is fertilized by a

sperm; no new, unique DNA identity is created; no embryo is implanted in

an uterus; no pregnancy results. Biomedical SCNT creates cell life, but not

human life: renewed cells, not new people. They certainly have no organs

that we could harvest—including, importantly, no brain, nor even the be

ginnings of nerve cells. We no more "kill" a blastocyst produced by SCNT

when we derive stem cells from them than we "kill" a vat full of replicating

skin cells when we throw it out at the end of an experiment. Fundamentally,

SCNT would be the basis for therapies that cure you with your own cells,

restored to the potential they had in their first moments of existence by the

power of the stimulated human egg.

Because they derive from the patient's own DNA, SCNT cells are an

exact genetic match to those in your own body, and are treated as "self" by

your immune system. 3 4 Whatever may emerge from further research with

ESCs derived from surplus embryos left over from IVF, SCNT cells offer a

virtual guarantee of freedom from the specter of rejection, graft-versus-

host disease, and a lifetime spent on toxic immunosuppressive drugs.

In preliminary, preclinical research, the new regenerative powers of

cells derived from SCNT have already shown their promise. In animal

models, SCNT medicine has already been used to cure many of the devas

tating conditions for which human treatments must still be found, such as

Parkinson's disease, 3 5 heart attack damage, 3 6 and the animal equivalent of

the "bubble baby" syndrome (SCID)—rescuing not mere weanlings, but

fully developed, adult organisms that had suffered with the disease for their

entire lives. 3 7 As we've seen, the ESCs taken from more conventionally gen

erated blastocysts have worked some of the same marvels—but some of

these studies suggest that, even where rejection doesn't happen, SCNT may

still provide some advantages. And indeed, the results tend to downplay the

therapeutic potential of SCNT, because in these studies the scientists have

not actually derived the cells from each animal individually so as to provide


a perfect match (as we would do for human patients), but have used one

line of cells to treat an entire colony of close cousins.

In the Parkinson's study, for instance, the researchers coaxed SCNT-

derived cells to produce neurons suited for use in several areas of the central

nervous system (forebrain, midbrain, hindbrain, and spinal cord) and re

sponsible for a broad range of functions. Some of them were the kind that

produce the neurotransmitter dopamine, which is involved in fine motor con

trol; as I noted, it's the loss of these cells that causes Parkinson's disease. Oth

ers were cells whose central functions involve another neurotransmitter

called choline, and whose loss is characteristic of Alzheimer's disease. They

were also able to derive cells that secrete other neurotransmitters in the brain

( se ro ton in and GABA); that carry movement-control signals from the spinal

cord to the muscles (and whose degeneration is central to motor neuron dis

eases); and that act as "support" cells to neurons proper, nourishing and pro

tecting them. This was a much wider range of mature cells than had been

successfully derived from previous protocols using conventional ESCs.

The team then put these cells to the test in the Parkinsonian rodents

(whose dopamine-producing cells had been knocked down to less than a

third of their healthy numbers by a toxin), comparing their effects to ESCs

derived by the conventional route. Dopamine-producing neurons derived

from either protocol formed solid, stable grafts, and improved behavior in

their recipients, and there was no sign of rejection of either type of ESC.

But even though the SCNT-derived cells came from recipient animals'

cousins rather than their own, individual bodies, these cells performed bet

ter than conventional ESC cells, forming larger grafts in their brains, with

double the number of transplanted nerve cells surviving eight weeks after

transplantation, and the final graft sites containing about 50 percent more

dopamine-producing neurons.

And it appeared that they might have been somewhat more effective

at restoring function, too. Because all the damage had been inflicted on

one side of the brain, chemically stimulating the remaining dopamine-

producing cells in the brain caused an imbalance in their motion, with the

larger number of intact cells on one side of the brain sending out stronger

signals to the legs they control than the more damaged side does. The result

was that the animals began to veer to one side, rather like what happens

when you push a shopping cart that has a damaged wheel on one side of it.

This "rotational behavior" is a key test of the function of the damaged part

of the brain. Treating these animals with dopamine-producing cells derived

either from conventional ESCs or ESCs created using SCNT reduced this


aberrant motion by more than 70 percent, with a hint that the SCNT-

derived cells were more effective (see Figure 3).

Because the range of neurons and supporting cells produced using

these protocols was so broad, the researchers who performed the study be

lieve that their technique could also be used to treat multiple sclerosis and

other "demyelinating" disorders (in which the myelin sheath essential to

the correct function of neurons is damaged or destroyed), Huntington's

Figure 3. Embryonic stem cells, and especially SCNT-derived cells, restore normal motion in a Parkinson's disease model.


disease, amyotrophic lateral sclerosis (Lou Gehrig's disease), and other mo

tor neuron diseases.

There remain technical hurdles to overcome in developing SCNT, but

theoretical objections to their ultimate use in human medicine continue to

fall. There have been concerns about the mitochondria in these cells, for one

thing: SCNT is achieved by replacing the DNA in an egg cell with a patient's

DNA, but this still leaves the egg's own energy factories providing the juice to

keep things going. Many researchers have therefore been concerned that the

resulting cells would be dysfunctional due to a mismatch between these mi

tochondria (created originally from the egg donors nuclear and mitochondr

ial DNA) and the final cell, or that the patient's body might reject the cells

based just on the immune-sensitive parts of the transplanted mitochondria.

So far, however, it doesn't seem likely that this mitochondrial mismatch is go

ing to trouble us. Aside from the fact that these cells have been incorporated

successfully into the patient-animals' bodies without any signs of rejection in

studies so far, a very careful study that looked all the way down at specific

proteins that are used to monitor for mitochondrial "foreignness" found that

the cells were accepted as completely native by all available measures.

Similarly, there are concerns that the "epigenetics" of SCNT-derived

cells—the "scaffolding" around the genes in the DNA code, which regulates

the expression of those genes—would be abnormal, leading to cancer or

dysfunction. Again, however, while this has been a problem with using em

bryos created using the nuclear transfer technique for making cloned ani

mals, it has not yet appeared to prevent stem cells derived from SCNT from

functioning properly when transplanted as a treatment into animals. And

indeed, early in 2006, scientists from the Whitehead Institute for Biomedical

Research in Cambridge, Massachusetts, reported that stem cells derived

from SCNT have identical patterns of being transcribed and turned into

proteins as do ESCs created by conventional IVF-type fertilization, with any

differences attributable to the genetic differences among the animals donat

ing the cells rather than the kind of cell involved. 3 8 Moreover, it appears that

the very process of generating stem cells from SCNT blastocysts of necessity

imposes a kind of "survival of the fittest" of its own, with any epigenetically

inappropriate cells collapsing under their own dysfunctionality; this may ex

plain a large part of why it's been so difficult to get a high yield of such cells

from a given blastocyst. This might pose problems for anyone actually look

ing to use nuclear transfer to clone a person (a point that should itself relieve

those concerned about such a use of the technique), but it appears that


epigenetic problems will only make the use of SCNT for medicine more dif

ficult, not prevent its safe and effective use.

Another open question is where we l l get all the eggs we l l need to use

SCNT widely as an anti-aging therapy. The supply is limited by the number

of women prepared to donate their eggs, and the hormone treatments and

moderately invasive surgery needed are likely to continue to keep the num

bers of such women down for some time. Many people also raise ethical

concerns about offering money or other inducements to solicit more

donors, especially for a procedure which is not without risk.

Even this, however, may yet be overcome on a technical basis instead of

a sociopolitical one. One option would be to take the eggs from other

species. Such an approach would not be without technical hurdles: notably,

the presence of mitochondria in such eggs that are not just from a different

person, but from a different species, might make the cells unable to create

and sustain an energy supply. With my background in mitochondrial biol

ogy, I recently proposed a solution to this problem should it arise. 3 9 My so

lution results in the mitochondria of the eventual ESCs being derived from

the eventual recipient of the cells, just like the nucleus, so it also avoids the

"intra-species" mitochondrial problem I mentioned above.

Another alternative may be to mass-produce egg cells bioengineered

from more common cell types, such as skin. Canadian researchers recently

reported 4 0 having used skin cells from fetal pigs to produce cells which

look—based on gene expression patterns, cellular structure, and some

functional abilities—an awful lot like egg cells. Whether these cells have

the full range of functions of egg cells remains to be seen, but they—or a

more developed version of them—might have the same power to reset the

clock in mature somatic cells that conventional eggs do. This would mean

that we can bioengineer an almost unlimited source of eggs: human fetal

skin tissues, which contain nineteen billion such cells per square inch. Such

huge numbers would allow us to avoid entrapment in the battlefields of the

culture wars, if we can simply reach agreement on the use of tissues from

stillbirths rather than aborted babies.

Frozen Embryos, Frozen Science

This brings me back to my second SENS scientific conference. At the time,

you could still smell the ozone in the air from the second in a pair of scientific


lightning strikes from a previously obscure group of Korean scientists from

Seoul National University, headed by veterinarian Hwang Woo-Suk. A few

years after Dolly the sheep, Hwang had claimed to have cloned a cow, and

more recently a dog, but his fame came when he announced in the winter

of 2004 that he had achieved the world's first derivation of fully fledged hu

man ESCs using SCNT. This proclamation rocketed him to international

fame, but it was just the beginning: a little more than a year later, in the

months leading up to SENS2, he reported a dramatic improvement on the

technique. In his first report, Hwang had only been able to derive a single

stem cell line from the 242 eggs that had been donated—and this line had

been taken from an egg fused with DNA taken from the egg donor herself,

which was of very limited biomedical use. Now, Hwang was saying that he

had created eleven human lines using only 185 eggs, and using DNA taken

from completely different people, including potential patients of both gen

ders and many age groups.

Everyone in the field, as well as the popular press, hailed this result as

a phenomenal breakthrough, and I was far from alone in seeing its poten

tial for treating not only age-related disease, but aging damage more

broadly. I knew that I would want someone to present not only Hwang's

results—with which most attendees would be at least peripherally familiar,

due to the enormous press coverage—but what they would mean for scien

tists working in the field.

Hwang's result was clearly going to have an enormous galvanizing ef

fect on stem cell research. Because of the political climate in which it had

taken place, the impact of the announcement was far greater than could be

accounted for by the purely technical breakthrough (great as it might have

been) of actually being able to make customized stem cells for healing pa

tients. Stem cell research had been stymied for years by President George

W. Bush's notorious decision, in the summer of 2001, to limit federal gov

ernment funding of stem cell research to work done using lines created

prior to the morning when he announced the policy.

That decision reversed a policy accepted under the Clinton administra

tion, but not yet implemented, that would have plowed NIH funds into

ESC research using lines derived either from IVF clinics or from work orig

inally performed with private funds. It came not out of science but from the

political maelstrom of the abortion debate, and the antiabortion stance

held by President Bush and by his key constituency of the Christian Right.

And while it is not accurate to call that executive fiat a "ban" on ESC re

search, it created an enormous chill over the entire field—and not just


because of the direct effects of cutting off funding for research performed

on nearly all available ESC lines.

The most obvious problem was the stranglehold it put on direct U.S.

federal government funding for embryonic stem cell work. The administra

tion holds the purse strings of a remarkably large share of U.S., and even

global, basic research in science, with US$20 billion in research-related

funding coming out of the National Institutes of Health alone each year.

Bush and his political allies would argue that their policy provides scientists

with plenty of opportunity to work with stem cells because of the availabil-

ity of the approved lines, but that claim ignores the actual state of the lines

in question.

The White House originally announced that their policy would allow

scientists to work with as many as seventy-eight robust stem cell lines, but

when senators put the question to NIH Director Elias Zerhouni, he admit

ted that only nineteen of these lines were actually viable, available in prac

tice (as opposed to locked up by intellectual property restrictions and

similar constraints), and ready for use in stem cell work. By 2004, this num

ber was still no higher than twenty-one. In preliminary research presented

at the National Academy of Science on October 12, 2004, fourteen of the

lines tested by Carol Ware at the University of Washington were found no

longer to grow well and to be hard to separate because of the outmoded

way in which ESC lines were derived and cultured at the time. One such

line was actually withdrawn from scientific use because of this finding. 4 1

A supply of just twenty-odd lines also fails to represent the genetic di

versity of humanity well, so it's hard to verify whether a given finding is a

quirk of that line or, say, of people of a given race. A supply of hundreds of

viable ESC lines is the likely minimum for healthy progress in this field of

science. Indeed, the present situation is worse than this: because of their

age, these lines are accumulating mutations that could skew the results of

research performed with them because they no longer even represent the

stem cells of those original donors. It also means that we can't study the stem

cells of people with particular diseases, or how experimental drugs affect

those processes—studies that would best be done with SCNT, which

would let us take the cells of people already known to suffer with a given

disease and wind back their clocks to the first moment of their primitive ex

istence as blastocysts. Researchers could then watch the cells as they under

went differentiation into the cells most affected by the disease and then the

late-phase changes that happened as their abnormal metabolism inter

sected with aging processes that happen even in healthy people's cells.


And not only are the cells of very limited use for basic research: every

one working in the field recognises that these cells will never be usable for

actual therapies either. All the lines that are both approved and available

are useless for clinical purposes because they were originally cultured using

feeder cells taken from mice—supporting cells needed to secrete factors

and provide structural support that is essential to keeping them in their pri

mal, unspecialized state. Contact with these cells has tainted them in vari

ous ways: one study 4 2 found that their cell surfaces contained a sugar that

the body's immune system recognises as foreign and attacks, and it's widely

expected (though not yet proven) that they may also contain mouse cell

proteins and even viruses.

It's only been in the last couple of years that scientists have developed

new techniques that first allowed for the propagation of human ESC lines

from human feeder cells, and most recently ESCs generated using no

feeder cells at al l . 4 3 And, again, it's at least possible that nothing short of

custom-made ESCs produced specially for the patient with SCNT will fully

address the potential problem of rejection. Thus, only ESC lines derived

well after the 2001 line-in-the-sand can actually be used as medicine for dis

ease and for the full repair of aging damage in the future.

The policy also ripples out well beyond the labs of people actually

working with the approved lines. For one thing, the restriction on provid

ing money to unapproved stem-cell work is so aggressively enforced that

the NIH has to snatch away grant money awarded even for research com

pletely unrelated to ESCs, if any of that money goes into facilities or equip

ment also used for work on "banned" ESC lines. You could be testing a

cancer drug on rats and have your funding pulled if someone else on cam

pus were sharing the use of gene-expression array equipment with you and

were using it for ESC work using lines not approved under the August

2001 decision. That makes it enormously difficult for anyone to carry out

work on ESCs other than the sanctioned lines on most university cam

puses, or in essentially all government research centers. Laboratories in

which sanctioned work does take place must expensively duplicate and

track equipment, all the way down to sticking colored dots on petri dishes

and other glassware, and must generally work in ways that degrade effec

tiveness.

The policy also erects enormous roadblocks even to privately funded

research—research that, in theory, is not the target of the Bush policy. Sci

entists in industry are first trained in universities, and when those universi

ties can't carry out ESC work, because of a mixture of lack of federal


dollars and the handcuffing of non-ESC work carried out using shared

equipment with work on "forbidden" lines, young researchers don't get

trained in the techniques of working with stem cells, let alone get the op

portunity to perform original research that would advance the field. This,

of course, means that such researchers aren't available for hire by private

firms even if they had the money to bring them on.

And naturally, the political uncertainty swarming around stem cell

work makes potential investors reluctant to pour money into companies fo

cused on developing ESC-based cures. At the time, it seemed possible that

the United States would follow other countries in making aspects of this

research—such as SCNT—not merely ineligible for government funding

but actually a criminal act. Investors will stomach most risks, but not politi

cal risk, and so they abandoned private-funded ESC research for a number

of years.

It briefly seemed likely that the Bush administration's policy would be

quickly brought down by political pressure. Even a very conservative selec

tion of polls shows that the majority of people in the United States and else

where are in favor of a fairly open policy on scientific access to ESCs. Even

in surveys in which the question is posed flat-out with no mention of po

tential human benefits, the majority of people say that they support deriv

ing stem cells from surplus embryos from fertility clinics for scientific

research. 4 4 When the question mentions the potential for human treat

ments, this proportion climbs into the 70 percent range. And most people

even support SCNT research—a fact that fills me with optimism about

their future acceptance of other anti-aging therapies.

So, in the August heat, with the controversy raging and President

Bush's popularity resting on unsteady ground, it seemed possible that pub

lic opinion would mobilize against the restrictive policy, and scientists

would within reasonably short order be enabled to work with ESCs from a

wide range of sources.

Then, the planes hit the World Trade Center.

In a month, everything had changed. Where ESC research had been

front-and-center on the national stage in August, it was off the radar screen

for almost everyone in late 2001, replaced by the immediate fear of terror

ism. As pressure and scrutiny from the wider public melted away, those

whose organization, resources, and ideological investment were strong

enough to continue to push their agenda on the subject even in the shadow

of the ruins of the Twin Towers suddenly became the only voices pushing

legislators—and in this case, because of the conflation of the science with


the abortion debate, that meant almost entirely forces opposed to ESC re

search. Anti-abortion groups, who are well organized and well funded,

made their case to Washington as strongly as ever, without the usual bal

ancing force of either the public at large or of their usual opponents: pro-

choice and civil liberties groups had no particular stake in stem cell science,

and the latter had their hands full with presenting the case for preserving

Constitutional rights in the face of the threat of terrorism. And while pa

tient advocacy groups might have stood in opposition to blockades on re

search, such groups were nascent at the time, and lacked the support from

pharmaceutical companies that often sustains them, since in this case the

companies had no vested interest in promoting the groups' cause.

Feeling deferential to a newly popular wartime president, handed

plenty of unba lanced misinformation by the anti-abortion activists on the

religious right that made up that president's base of support (and had

played a significant role in their own sweep into power), and with a leader

ship dominated by representatives with a social-conservative worldview of

their own, the Republican-dominated Congress substantially raised the

threat against stem cell science. Parallel bills introduced by Sam Brown-

back in the Senate (S 245) and Dave Weldon and Bart Stupak in the House

(HR 234) sought to ban all forms of "human cloning"—including SCNT

performed entirely for scientific or medical purposes.

These measures would not only deny federal funding to, but criminal

ize, the creation of blastocysts using SCNT—imposing actual jail sentences

on scientists performing the work. They would also have imprisoned scien

tists doing any scientific research using ESC lines derived from SCNT; in

the original texts of these bills, this went so far as to threaten both doctors

and patients with prison time if they administered or accepted cures using

SCNT-derived stem cells. Some language even suggested that people who

went abroad to receive treatment with SCNT stem cells could be penalized

for it on their return to the United States.

But in the coming months, as the public slowly began to raise their

heads out of their foxholes, proresearch and patient activist forces began to

countermobilize. They were greatly helped by the voices of prominent pa

tients suffering with diseases likely to benefit from SCNT and those close

to them, including Michael J. Fox (Parkinson's), Kevin Kline (whose son

has juvenile diabetes), Christopher Reeve (spinal cord injury), and, most

powerfully, Nancy Reagan (whose husband, the former president, died of

Alzheimer's disease). A bipartisan coalition favoring expanded embryonic

stem cell access—and in many cases the full legalisation of biomedical


SCNT—began to form, including such prominent anti-abortion Republi

cans as Orrin Hatch, Strom Thurmond, Arlen Specter, John McCain, and

ultimately then senate majority leader Bid Frist, and apparently extending

even to Bush's own secretary for Health and Human Services, Tommy

Thompson. Meanwhile, prominent scientific organizations (including the

National Academy of Sciences, the American Medical Association, the As

sociation of American Medical Colleges, and even the National Institutes

of Health itself), as well as multiple disease-specific charities (such as the

Juvenile Diabetes Research Foundation, the American Association for Can

cer Research, the Lance Armstrong Foundation, and the American Diabetes

Association) endorsed research using new ESC lines and the advancement

of work on SCNT.

Hatch's coalition introduced legislation to legalise SCNT for scientific

and medical research, while banning use of the technique as a means of

cloning people. They also introduced legislation to allow access to surplus

embryos from fertility clinics as a source of stem cells. Slowly, more and

more legislators from both sides of the aisle signed on to the pro-research

side of the debate. For the next several years, the two forces fought to a

standstill, with both bills repeatedly introduced and defeated. This created

a legal and scientific limbo that ultimately served the anti-research camp's

agenda: the few scientists working on SCNT remained out of prison but

without access to funding, potential private investors continued to wait out

the political uncertainty, and the President's restrictions on ESC research

remained in place.

False Dawn

Then suddenly, in 2005, came Hwang's announcement of relatively high-

yielding techniques for creating individually tailored ESCs. The news acted

like a juggernaut, smashing through barriers both scientific and political.

Technically, the ability to make viable, customized embryonic stem cells tai

lored to individual patients was a massive breakthrough. Politically, it not

only reenergized pro-research forces, but applied a new source of pressure

on politicians. Stem cell advocates had long argued that, if the government

continued to keep a tight lid on ESC research, the science would be done

elsewhere: the United States would simply suffer a brain drain, as Ameri

can scientists moved to more hospitable climes to pursue their vital work

and as foreign graduate students (already chafing under new security


restrictions) refused offers from American universities. Now, the prophesy

began to come true. The Korean government was ready to back their new

scientific star's work with significant resources; countries as far-flung as the

United Kingdom, Israel, Sweden, and Singapore began establishing them

selves as well-funded hubs for ESC research; and reports of prominent sci

entists packing their bags started appearing in the media.

The forces of competition began to work their usual magic. Individual

U.S. states, fearful of being left behind, began putting up bills to fund stem

cell research within their own borders. Federal politicians not strongly ideo-

logically committed against ESCs—including many free-market-oriented

Republicans—became increasingly willing to challenge the agenda of the

antiresearch ideologues. A couple of years earlier, fifty-eight senators—most

of them Democrats, but with substantial support from key Republicans—

had signed a letter asking Bush to rescind his policy; a little over a month af

ter Hwang's announcement, 206 House members followed suit.

I knew that highlighting these advances, and the opening that they af

forded to researchers, would be a great way for me to further my confer

ence's mission to promote anti-aging biomedical research. Short of Hwang

himself, the best person to present the opportunities was Gerald Schatten, a

stem cell researcher at the University of Pittsburgh who had been working

with Hwang for the last two years, had used his veterinary techniques to

clone a monkey, and had signed off on the paper announcing the new SCNT

lines in Science. I asked him to present their results and outline the royal

road to accessing patient-specific ESCs through Hwang's team at Seoul Na

tional University: a "World Stem Cell Hub" that would generate SCNT cells

to order using Hwang's established facilities and exper ienced technicians.

I was delighted when Schatten accepted my invitation—but I was pos

itively overjoyed when, not long after, he came back with another e-mail

saying that he'd like to bring along a friend. Hwang himself had expressed

an interest in presenting at SENS2, he said; he realized that it was short no

tice, but would I be willing to let him share Schatten's own half-hour slot in

the conference? I, of course, offered instead to give Hwang his own half-

hour talk as a featured presenter in the session on stem cells and regenera

tive medicine. I'd have been happy to do this even if it had required

throwing out my original schedule and starting from scratch, begging for

giveness from presenters as I shuffled them around at so late a stage in the

planning of a very packed conference schedule; but fortunately I didn't

have to do this, as another presenter had recently been f o r c e d to pull out.

With hardly any shuffling, Hwang was confirmed.


So it was that, with great pleasure on my part and keen attention from

hundreds of my colleagues, Hwang mounted the lecture podium of Cam

bridge's Fitzpatrick Lecture Hall.

Of course, as you know full wed, unless you spent much of the winter

of 2005-2006 in a cave in Nepal, it was all a sham. Within months of elec

trifying my scientific audience in September, Hwang had been exposed as a

fraud.

Bad Wizards and Bad Men

First there were ethical questions about the sources of Hwang's eggs; then,

questions about the viability of four of the eleven stem cell lines that he had

submitted to Science. And then, reporters looking at photographs presented

with Hwang's data began to notice some suspicious resemblances between

allegedly unique stem cell lines. Hwang brushed these off as the result of a

confusion with the Science production staff about which of the numerous

photos that he had submitted were to be used as figures in the article.

The case against Hwang quickly picked up momentum. Scientists re

viewing the paper's data n o t i c e d suspect similarities in the genetic profiles

of the various lines' cells. Then Schatten requested that his name be retro

spectively removed from the paper's authorship because of "allegations

from someone involved with the experiments that certain elements of the

report may be fabricated." And on December 15, one such collaborator

came forward with the flat statement that nine of Hwang's eleven lines were

flat-out fakes, sharing identical DNA with one another, and claiming that

Hwang himself had admitted the fraud.

As each doubt was raised, Hwang would protest his innocence, variously

blaming errors, contamination, and the incompetence of others for each of

them—even going so far as to claim that one former collaborator had

"switched" some of his lines. But, eight days after his former collaborator

claimed fraud, he proffered his resignation to Seoul National University—

which was refused, on the grounds that he was now the subject of an internal

investigation. He was suspended in February, dismissed in March, and in

dicted in May for fraud, embezzlement, and violation of bioethics legislation.

The fallout of these revelations was felt at many levels. There was, of

course, enormous outrage at the fraud, and great disappointment that

Hwang's breakthrough turned out to be flimflam. And it was a political fiasco,

exploited by anti-ESC campaigners to cast aspersions on the entire field.


But Hwang's fraud had also set the progress of the entire field back by at

least a year—an eternity in science. The Bush restrictions on ESC research,

amplified by the looming threat of criminalization for SCNT from the Amer

ican Congress, had kept all but a few research teams from working to perfect

nuclear transfer for human patients. Hwang's claims had further diminished

the incentive to put resources into the goal: No one wanted to reinvent the

wheel already spinning in Korea, and private firms would no longer have a

competitive edge as the first creators of patient-tailored ESCs, using in-house

methods that could be kept exclusive as trade secrets or through the patent

process.

One private firm, A d v a n c e d Cell Technology (ACT), had been coura

geously soldiering on with the work, producing a great deal of quality ESC

and SCNT science (much of it, admittedly, overplayed in the media)—this

despite constantly lurching from one financial crisis to the next because of in

vestors skittish over the legal climate of their research. In late 2001, they fa

mously announced the first "cloned" human blastocyst,4 5 although the DNA

that was transferred into the egg cell came from the donor's own body—in

fact, from cells that normally enshroud the egg itself—and the resulting blas

tocysts couldn't develop beyond a six-cell ball. They spent much of the next

two years perfecting that technique, issuing many publications (most of them

on research done in cattle) charting their progress toward teasing out the rea

sons for the low yield of viable blastocysts in SCNT techniques, and working

steadily to perfect the technique for human biomedical use.

In late 2003, insists ACT scientific director Robert Lanza, they were

very close to resolving the sticking points in their technique, and could

shortly have generated the first viable stem cells tailor-made for patients or

for research on specific diseases. With Hwang's eleven-cell-line announce

ment, however, investors began pulling their bets out of what was perceived

to be an "also-ran" in the race—a blow turned into a haymaker by ACT's

simultaneous setback of losing their main source of human eggs. Cells were

put into deep-freeze, and ACT's human SCNT work shut down.

Equally infuriating is the case of Professor Alison Murdoch and Dr.

Miodrag Stojkovic, of the Newcastle Centre for Life, a fertility clinic and

research center in Newcastle-upon-Tyne in Britain. These researchers man

aged to create the first human SCNT blastocysts using DNA taken from

the cells of a person other than the egg donor. 4 6 Like the ACT cells, these

blastocysts were not fully viable, but in the United Kingdom's more

research-friendly environment, the group had received formal approval

from regulatory bodies to pursue work using SCNT-derived stem cells, giv-


ing them the green light to perfect their technique. But their publication

came on the heels of Hwang's, and compared to his explosive success, the

creation of only three fused cells that actually began dividing, and no actual

stem cell lines, seemed to be of no relevance to the progress of the field.

They, too, promptly shut down their research on the technique—a decision

that Murdoch says cost them at least a year.

It was the same story elsewhere. SCNT research teams in Sweden, and

also at three American universities that had raised enough private or state

money to set up stem-cell research centers with elaborate financial firewalls

separating them from federally funded research elsewhere on the same

campuses, either dropped their efforts altogether or put them on hold

while waiting to see whether the Korean team's plans would make their ef

forts redundant.

But if Hwang's shot, heard 'round the world, turned out to be a backfire

at best, it still served to wake up a lot of people. All over the globe, and es-

pecially in the United States, researchers began thinking seriously again

about what they could do once they had access to the Korean team's expert

ise. It promised stem cells with the miraculous flexibility of the blastocyst,

but perfectly matched to patients suffering with the worst of the nightmares

of aging: Parkinson's disease, stroke, scarred and weakened hearts, eyes

blinded by the death of light-sensing cells choked in their own waste, limbs

withering away as the electrical sparks stopped flowing through nerve cells

or muscle cells snapped one by one under the force of their own molecular

decay. Labs began contemplating grant proposals. Young science students

turned back to stem cell research as an exciting career prospect. The dawn

was false—but its rays woke the slumbering forces of science all the same.

Today, after the collapse of Hwang's house of cards, and in defiance of

the Bush administration's politically driven, morally misdirected obsti

nacy, the field is undergoing a renaissance. Murdoch and ACT have fired

up their programs again. Teams are in hot pursuit of successful SCNT

techniques, and the research and cures that they will enable, all over the

world. Cutting-edge work is occurring at the Center for Regenerative

Medicine at Edinburgh University, Scotland (taking over clinical research

from the veterinary work that created Dolly the sheep); at the Karolinska

Institute in Sweden; at Shanghai Second Medical University, China; and at

several privately funded centers in the United States, including the Harvard

Stem Cell Institute, the University of California at San Francisco, and

UCLA's Institute for Stem Cell Biology and Medicine.

The legal climate is shifting, too. In addition to China, Great Britain,


and Sweden, SCNT is already explicitly legal in Singapore, Belgium, Japan,

Spain, and Israel. And it remains legal in the United States, despite the ef

forts of Senator Brownback and his allies: the Brownback-Weldon bill has

twice faded to make it through Congress, though it was reintroduced in

2005 as S 658/HR1357, the Human Cloning Prohibition Act of 2005. More

excitingly, Orrin Hatch's bipartisan Stem Cell Research Enhancement Act,

which would have opened up ESC research using lines derived from IVF

surplus embryos, passed both the House and the Senate, and was only

blocked from becoming law by a Presidential veto—the first of Mr. Bush's

six-year administration. Hatch's pro-SCNT bill is also back in play, al

though no vote is imminent.

Meanwhile, individual U.S. states are moving ahead, doing their best to

sidestep the funding and regulatory vacuums at the federal level. SCNT re

search has been legalized in California, Connecticut, New Jersey, Rhode Is

land, Illinois, and Massachusetts, and although several other states have also

specifically prohibited all SCNT work, many more are permitting work done

using surplus IVF blastocysts. A ballot initiative in Missouri that would con-

stitutionally protect scientists' ability to conduct ESC and SCNT research,

and patients' ability to access cures based on these techniques that are avail-

able anywhere else in the nation, narrowly passed in November 2006.

The states are also digging up the funds needed to get work going in

side their own biotech sectors. The most famous of these is California's

Proposition 71, a ballot initiative that established the California Institute

for Regenerative Medicine and gave it a bond-funded budget of $3 billion

to fund ESC work including (but not exclusive to) SCNT research. The ac

tual disbursement of these funds has so far been bogged down by anti-

research legal actions and some legitimate questions about oversight and

ethics, but legal rulings have been almost uniformly favorable, and Gover

nor Arnold Schwarzenegger has recently stepped in with a bridging loan,

to start the Institute's mandated dollars flowing toward development of

SCNT- and other ESC-based cures.

And if California is the most famous case, it is far from the only one—

or even the first. That honor goes to New Jersey, which in early 2004 be

came the first state to earmark state funds for ESC research. Starting in

December 2005, New Jersey has put out a total of $5 million in grants

awarded to seventeen research institutions for research on stem cells from

embryos and other sources, and has set up the $23-million New Jersey Stem

Cell Institute. Similar initiatives are starting up in Connecticut, Illinois,


Maryland, Massachusetts (despite a faded veto attempt by the state's gover

nor), and the state of Washington.

Meanwhile, efforts have been under way in the private sector, despite

the lack of support, adverse regulation, and a climate of uncertainty that

sends all but the steeliest of investors off in search of other opportunities.

ACT is one prominent example; another is Geron Corporation, a biotech

company most famous for its work on the "youth enzyme," telomerase

(which it is now seeking to manipulate in order to shut down cancers by

turning off the telomerase taps—see Chapter 12 for much more on this).

Geron has perfected methods of raising human ESCs without feeder cells,

and is testing six different lines in animals; excitingly, it expected to be

ready to begin the earliest stages of human trials using neural stem cells for

spinal cord injuries in the spring of 2007.

Some scientists are also seeking purely technical ways to liberate sci

ence from the phony moral dilemma surrounding the use of blastocysts for

research into, and as cures for, human disease. There are multiple proposed

ways to create ESCs from blastocysts without eliminating the potential for

these cell balls to ultimately become human lives. One is parthenogenesis, a

label taken from the technical term for "virgin birth." In this technique, the

genes in an egg cell (which naturally contains only half of a full comple

ment, as it is designed to be augmented by those in the sperm cell at fertil-

ization) are doubled up on themselves, thereby generating a complete set of

DNA instructions; this allows the egg cell to behave enough like a blasto

cyst to produce ESCs for the egg donor, without actually fertilizing the egg.

Another approach is to take stem cells from IVF clinics' embryos that have

defects preventing them from going forward to make a fetus, or to actually

induce such defects into a patient's DNA before making a blastocyst from it

using SCNT, in order to eliminate even its potential to form a human life.

Recently, ACT introduced yet another option: using stem cells derived

from a single cell plucked from the blastocyst, while leaving the rest of them

in place as a potentially viable embryo (as is already sometimes done for

genetic testing of IVF embryos before implantation). 4 7 Yet a fourth possi

ble option is to coax adult stem cells into behaving more like embryonic

stem cells, using growth factors and other chemical messengers, instead of

using the inherent renewing power of the egg to do the same thing. 4 8

I have no doubt that such work is valuable—but primarily because it

will tell us more about stem cell biology. The lessons learned will allow us

to manipulate ESCs and SCNTs more capably when the legal environment


finally unleashes the scientific racehorses, champing at the bit to bring the

promise of these cells to fruition. The specific techniques involved will

probably not, and most certainly should not, be necessary to bring cures to

patients with "official" diseases or to regenerate human bodies deprived by

the aging process of their capacity to self-heal. Their perceived necessity is

a purely political construct, unrelated to scientific reality or underlying hu

manitarian need. The real need is to free scientists from misguided interfer

ence with the quest to turn the enormous potential of embryonic stem cells,

including patient-specific cells created by fusing a patient's cells with an

egg, into therapies for the sick and the old.

Fortunately, this is one area where nearly all my colleagues already es

sentially agree with me—and not just in biogerontology, but across the

medical and basic biological science world. The grant-review scientists at

the National Institutes of Health would be delighted to disburse funds to

promising ESC and SCNT research around the nation, if their hands were

not bound by their president's executive orders. Everyone not under the

blinders of a mi sp laced sense of moral responsibility to a ball of cells recog

nises the need for ESC research guided by responsible ethics and regula

tion, not artificial restrictions created out of confusion, fear, and the grasp

of political opportunity.

Certainly, there are scientific hurdles to be overcome before ESCs can

be used directly as medicine. We have to develop much more reliable tech

niques for deriving stem cells, transforming them into the kinds of cells that

we need, and making them play the same full range of roles that the corre

sponding cells growing under the guidance of sophisticated developmental

programs within our bodies already do. The nascent field of regenerative

medicine is already making surprising progress even using cells and tissues

grown from patients' adult cells: tissue engineers are moving from cells to

organs, seeding cells into a biodegradable scaffold that guides them to form

into a structurally appropriate engineered tissue and then melts away, leav

ing functioning tissue behind. 4 9 Human patients have been given functioning

urethras, starting with cell-free structural tissue taken from cadavers and

seeded with the patient's cells, which have lasted seven years. Functioning

bladders have been engineered and transplanted into Beagle dogs, and rab

bits have received, and successfully used, engineered erectile penis tissue.

And in the most ambitious work to date, cattle have been given simple kid

neys created using SCNT, with DNA taken from an ear clipping. The reju

venated cells were expanded, growing to fill in every cranny of a complex

biodegradable kidney scaffold, and the resulting organ implanted. The ar-


tificial kidneys were functional, filtering the blood and producing a fluid

with close chemical similarity to normal urine.

But the fundamental impediment to the dream of new cells to replenish

bodies worn by the years or by disease is a political one—and so must its so

lution be.

Action Now for Science and Medicine

Nearly all the anticipated readers of this book are citizens of democratic

states. A few live in countries that have already given their scientists the

green light to pursue cures with ESCs within careful ethical and regulatory

frameworks. If so, congratulations. You can help to lead the race for cures

forward further by lobbying your politicians to increase funding for such

research.

But probably the single largest share of my readership will be in the

United States—the country that still makes the greatest contributions to

world scientific progress, where young scientists still flock to chase the ad

vancement of human capacity, and where government and industry funding

could, if unleashed, have the greatest impact on the field. The National In

stitutes of Health need to have the brakes taken off their funding power,

and to be allowed to step down on the accelerator—hard.

Your voice can help the scientific process along in a way that the sci

entists themselves can't match. Write letters, join lobby groups, educate

yourself about local issues and your Congressional representatives' posi

tions; then vote for pro-stem-cell ballot initiatives and research-friendly

politicians. Excellent background information and tools to help you sup

port favorable legislation are available from the Coalition for the Advance

ment of Medical Research (CAMR) at http://www.CAMRadvocacy.org.

You can bring forward the date when animal studies become clinical

cures—and when, eventually, the old grow young, their bodies renewed by

their own rejuvenated cells and tissues. Scientists need your help now to

bring medicine out of the lab and into the lives of suffering patients.

When you and your loved ones need their help, you will want to know

that you have done everything you could to support their lifesaving work.

http://www.CAMRadvocacy.org

12

N u c l e a r M u t a t i o n s a n d t h e

T o t a l D e f e a t o f C a n c e r

Apart from the small amount in our mitochondria, all our DNA

is housed in the nucleus of our cells. Like mitochondrial DNA,

it accumulates damage throughout our life, and this can

theoretically lead to innumerable health problems. However, I

believe that in practice only one of those problems—cancer—

arises within what we currently consider a normal lifetime.

Thus, if we could really thoroughly defeat cancer, nuclear

mutations would be harmless. The most audacious component of

SENS is just that—a way to defeat cancer altogether.

In a few places in earlier chapters, particularly Chapter 10, I've

whetted your appetite with regard to telomeres and telomerase. I know you

have that appetite, because when someone asks me what I do and I say I

work on combating aging, the commonest response (apart from the just

slightly predictable "Hurry up!") is "Ah, telomeres." And indeed, telom

eres and telomerase play a very prominent role in SENS. But not the role

that most of you are probably expecting.

As I've stressed throughout these chapters, the "engineering" ap

proach to combating aging is fundamentally different from conventional

thinking about aging and what to do about it, in that it focuses on the actual

damage that the aging organism accrues, rather than the metabolic processes

that cause that damage to accumulate.

This operational definition of aging makes the problem tractable. In

N U C L E A R M U T A T I O N S A N D C A N C E R 2 7 5

the old-school, "gerontological" approach, the number of potential con

tributors to the aging process is legion, and getting control of all of them is

a paralyzingly daunting task. It requires us to have a detailed understanding

of an enormous number of complex pathways, interference with any of

which is both difficult and bound to cause unwanted side effects as the nor

mal function of those pathways is perturbed.

Anti-aging engineering sets us largely free of these problems. We leave

metabolism to carry out its necessary but messy work, and find ways to

undo or render harmless the relatively small number of fixed changes—

molecular damage, in other words—that occur in the actual structure of

the aging organism as a result of those processes. We are left with a field of

just seven classes of damage to deal with—classes for which solutions are

foreseeable, and whose repair is unlikely in itself to cause any negative side

effects. All that we intend to remove is initially inert but eventually patho

genic (pathology-causing) damage—aspects of the aged body that the

young organism does just fine without.

There is, however, one apparently gargantuan hole in this logic, and

that is the question of damage to the DNA code in the cell's nucleus (as op

posed to the DNA held in the mitochondria, which I discussed back in

Chapters 5 and 6). Whereas mitochondrial DNA is responsible only for the

production of the energy factories in which it is housed, nuclear DNA is

the master blueprint from which our entire biological structure is built up

and maintained over time. The proteins 1 that it encodes not only make up

essential structural features of the body, from the lens of the eye to the

pumping muscles of the heart and the miles and miles of arteries that carry

blood to our cells, but also include tiny enzymatic machines that do every

thing from detoxifying poisons to budding up fatty membranes and carry

ing chemical signals from one cell to the next. Damage the DNA, and you

corrupt the code of our genetic program, or render perfectly good genetic

instructions unreadable by the machinery that transcribes them into orders

to be sent out to the body's protein-making "factories."

And your genes do suffer accumulating damage over time. The DNA

in the nucleus is subject to a continuous assault on its structure. Each cell's

nuclear DNA takes about a million damaging "hits" every day, caused by

everything from ultraviolet radiation and environmental toxins to the free

radical by-products of its metabolic processes. And even brand-new DNA

isn't necessarily pristine: when the cell replicates itself, errors perpetrated

by the machinery that copies the cell's genetic information often create

production flaws of varying degrees of seriousness.


Much of this mischief is quickly fixed by the cell's elaborate quality

control system for DNA, but some of it is irreparable by its nature. Some

other damage is potentially reparable, but becomes indelible if the cell di

vides before repairs are made. Such permanent changes are mutations, and

while mutations that occur elsewhere than in sperm and egg cells (and their

progenitors) will not be passed on to the organism's progeny, they will be

perpetuated in the cell in which they occur and in any of its "descendents."

On top of damage to nuclear DNA itself, there is damage to the so-

called epigenetic structures of our chromosomes—the "scaffolding" that is

anchored to our DNA. Epigenetic structures contribute important informa

tion by determining which genes are turned on in a cell and which are

turned off, allowing the same overall DNA to be used to create cells as di

verse as liver, heart, and kidney cells. Because of this, changes in the epige

netic scaffolding of a cell's DNA ultimately have the same range of functional

effects on the cell as changes to the genes themselves: By turning on genes

that should be turned off (or vice-versa), or increasing or decreasing their

activity, these "epimutations" change the complement of proteins produced

by the cell. Because they are operationally equivalent in terms of their im

pact on cell function, I'd allow myself a little terminological sloppiness to

avoid belaboring the point with extra verbiage. From here on, I'll mostly be

using "mutations" to refer to both these kinds of genetic damage—true mu

tations and epimutations.

Because they occur on an occasional, random basis and are permanent,

mutations accumulate with age—and therefore, they qualify as "aging dam

age" by the definition e m b r a c e d by the anti-aging engineer. The implica

tion, then, is that we will have to either fix them or render them harmless if

we're going to keep the body from progressively declining into pathology

over time.

It Is Broke. We Can't Fix It

Having read this far, you may be expecting that I'll propose a fix for muta

tions similar to those I've suggested for AGE cross-links, unwanted cells, or

lysosomes: just get rid of the junk. But a moment's reflection should show

that this can't be done. Damaged genes may be dysfunctional, but we can't

afford to just do without them: a cell with anything other than a functional

gene is still damaged. And that presents a daunting challenge—so daunting,

in fact, that for a time I despaired of its solution, and feared that mutations


would act as ship-smashing cliffs to any ark that we might build to survive

the deluge of metabolism and emerge into an ageless future.

So, you may think, If we can't afford to destroy defective genes, can't we

repair them instead? Unfortunately, this is a technical near-impossibility in

the foreseeable future, for the simple reason that there are so many differ

ent genes in the nuclear DNA. The human nucleus has two copies of nearly

all our genes; the aggregate size of one copy (the "haploid genome") is

about three billion "letters" of DNA. Exactly how much of this is really ac

tual instructions for building and regulating the body is a matter of some

debate, but certainly there are plenty of different places where damage to a

"letter" could cause the misspelling of a "word," leading to a loss of infor

mation that could harm the function of the cell. That's a lot of potential

damage that we would expect to need to fix.

The problem is how to do that for so many distinct genes. Any mecha

nism we might use to fix a damaged gene would have to somehow "know"

how to distinguish an intact gene from a damaged one. True, the body al

ready does this, by comparing the damaged DNA to its complementary

strand in the double helix (or sometimes to the homologous chromosome, i.e.

the other copy of the relevant stretch of DNA—remember I just told you that

most genes are present in two copies in each cell), but it's not clear that this

helps us much. It's hard to see how we could improve on our existing, inbuilt

ability to repair DNA, which in humans is already amazingly effective.

We could, in principle, solve this problem if our DNA-repair system

relied on a blueprint independent of the genetic information within the

cell. But this would require a molecular-level tool that would carry in it

self a master copy for each of the many tens of thousands of genes (each

of which is typically a thousand or more DNA letters in length). It's con

ceivable that advanced nanotechnology might somehow be able to pro

vide this level of detail to machines that could then carry out the repairs, 2

but only in the very distant future; we're nowhere near that level of profi

ciency today.

In fact, this summary actually understates the difficulty of the job we

would face if our solution to mutations were to fix them one at a time.

You're probably visualizing that these double-copy gene mutations are

nice, clean breaks cutting across the two strands of the DNA helix—and

sometimes they are. But sometimes, the DNA is either initially hit, or is mis

takenly "fixed" by the body, in a way that leaves two distinct errors on ei

ther strand, separated by a dozen or so DNA letters. This leaves gaps whose

repair, even given a proper blueprint, would entail first fixing the damage


to both sides independently and then realigning the two strands and zip

ping them back together.

This one ready had me stumped back in July 2000, at the conference

where the engineering approach to developing anti-aging biomedicine first

crystallised in my mind. If we can't just throw out damaged DNA, and

there's no clear way to fix all of the possible forms of permanent DNA dam

age that accumulate with age, aren't we stuck with a mechanism of aging

that we can't do anything about—and that will therefore kill us even if we

repair or obviate every other molecular and cellular change that con

tributes to aging? At first I essentially ignored the problem, relying that

other approaches to cancer would suffice, but I became increasingly doubt

ful that they would.

Who 's Afraid of the Big Bad Mutations?

Throughout these chapters, I've always explained how a given kind of molec

ular or cellular change ("damage") probably contributes to aging pathology.

But in most cases, it's not totally clear to what extent a given kind of alter

ation actually adds to the loss of function, increased disease risk, and expo

nential rise in death rates that characterise biological aging. In all the cases

we've discussed so far, however, the answer to this question doesn't ready

matter. Aging damage is, by definition, not a part of a healthy, youthful body,

so removing or obviating that damage certainly won't do us any harm—and,

from what we can ted, will almost certainly do us significant good.

In this case, however, I couldn't see a clear way either to repair or to

render harmless mutations in the nuclear DNA. So I had to take a step back

and ask a more fundamental question: Do we, as a practical matter, actually

have to worry about nuclear DNA damage?

Even to ask such a question sounds a bit crazy to some of my col

leagues. Because the nuclear DNA is so clearly critical to cell structure and

function, it seems beyond debate that mutations are a contributor to aging.

This concept was first formally proposed in the late 1950s, before we ready

even understood what genes were, and it has become almost universally ac

cepted by both scientists and the public at large.

But, however initially intuitive it may sound, this notion has never been

justified with direct (or even good indirect, i.e., correlative) evidence. The

only way to rule out something's involvement with aging is to speed it up

and observe no effect on life span or age-related pathology.3 This has been


accomplished for nuclear mutations, but not yet well enough to be decisive.

In mice, deleting a gene that normally fixes up free radical hits to genes be

fore they have a chance to go on to become actual, fixed mutations greatly

increases the steady-state level of such damage in the nuclear DNA. Yet

these animals appear to suffer no pathology as a result, and have normal life

spans. 4 However, we can't read too much into this result because the muta

tion rate is only elevated rather modestly. Similarly, a study was recently

performed using four strains of mutant mice, each with a knockout of a dif

ferent DNA-repair gene. In one such strain, mutations accumulated more

than in normal mice-—and yet, the effects on lifespan were unclear.5

A very good, and equally direct, test for showing that something is a

key contributor to aging is to slow it down or arrest it and observe a direct

anti-aging effect: an increase in the "natural limits" to the organism's life

span and the preservation over time of youthful functionality. Of course, no

one has ever done this with nuclear mutations, or indeed with anything

else. Unfortunately for scientific clarity, all the successful anti-aging inter

ventions that we currently know of in mammals change many things about

the organism, from antioxidant enzymes, to maintenance of proteins, to the

activity of the cell's garbage-disposal system. This prevents us from isolat

ing any one of those changes as the dominant cause of the anti-aging effect,

and thus isolating any particular type of damage as being the dominant

contributor to aging. Calorically restricted animals, for instance, lose a sig

nificant amount of bone mass, but no one thinks that this loss is responsible

for CR's anti-aging effect.

A close approximation of such a test, however, was published a couple

of years ago, in the form of mice that had been given genes allowing them

to produce extra amounts of an antioxidant enzyme (catalase), specifically

targeted to different parts of their bodies. 6 , 7 I mentioned these mice in ear

lier chapters, but the study is worth a recap. Catalase detoxifies an abun

dant oxidizing molecule (hydrogen peroxide), so it can potentially protect

things it's close to from at least one form of damage. Putting catalase into

these animals' mitochondria, which significantly reduced the development

of mitochondrial DNA deletion mutations, reduced their vulnerability to

several age-related diseases, and extended their maximum life span by

about 20 percent—the first unambiguous case of an antioxidant genetic in

tervention with an effect on this key measure of aging in mammals. Yet giv

ing these organisms catalase targeted to the nucleus, which reduced nuclear

mutations, provided no benefit in terms of lifespan.

Another type of evidence that is often raised in support of the idea of


nuclear genetic damage as a contributor to aging is the existence of so-

called "accelerated aging" models whose symptoms arise from accelerated

rates of nuclear mutation accumulation. These are animals either with vari

ous inborn mutations, or subjected to outside assaults (like bombardment

with toxic chemicals or X-ray radiation), that increase the accumulation of

nuclear DNA damage as they age, either by increasing the rate at which it is

formed or by knocking out the machinery that repairs it. This includes such

human genetic diseases as Hutchinson-Gilford syndrome ("progeria") and

Werner's syndrome.

Victims of these diseases, whether they walk on two feet or four, do often

look in many ways like the elderly, suffering pathology that can be eerily par-

allel to that seen as animals get older, from bone diseases and failing hearts to

scruffy fur and cataracts. But the fact that the symptoms of an abnormal

pathology look a lot like the symptoms of "normal" aging doesn't prove that

the mechanisms of one underlie the mechanisms of the other, any more than

a wet lawn proves that the same mechanisms govern rainfall patterns and

sprinkler systems. Almost anything that messes up normal equilibrium in the

body but takes a while to kid you will look like "premature aging;" the ques

tion is what if any relationship a given change bears to aging in the rest of

us. Evolutionary biologist Michael Rose, a geneticist at the University of Cali

fornia who has himself bred remarkably slow-aging, long-lived fruit flies,

puts the point succinctly: "A lot of people can kill things off sooner, by screw

ing around with various mechanisms, but to me that's like killing mice with

hammers: it doesn't show that hammers are related to aging."

Because we don't have this kind of direct evidence, we normally rely on

more indirect, correlative types of evidence of a phenomenon's involvement

with aging. One is to compare the rate of accumulation of some kind of

damage in animals that age at different rates (that is, operationally: whose

"oldest old" finally succumb to "natural" death, after first progressively

losing youthful functionality, at different chronological ages). While all ag

ing animals do accumulate nuclear mutations, the rate at which longer-lived

animals suffer free radical damage to the nuclear DNA doesn't correlate

well with their maximum life spans (unlike the corresponding rate in mito

chondrial DNA, which does).

Frustrating, isn't it? But the good news is that, in my view anyway, the

available evidence allows us to conclude with some confidence that nonspe

cific nuclear DNA damage is not meaningful contributors to aging. I briefly

summarized the argument for this conclusion back in Chapter 4; here's the

full story.

N U C L E A R M U T A T I O N S A N D C A N C E R 281

What gives force to the idea that nuclear mutations are a cause of aging

is the fact that the mutations we inherit from our parents are major risk fac

tors for a wide range of diseases, including age-related diseases from cancer

to heart attacks to Alzheimer's. The same is sometimes true of mutations that

occur very early in development, when there are so few cells in the little ball

that will eventually transform itself into a human body that damage to the

nuclear DNA of just one of them can infect almost our entire being with the

same flaw.

But the situation is quite different after we're born, which is when new

mutations occur and accumulate with the passage of time—and thus, where

we have to think about an effect of nuclear mutations as a form of aging

damage (as opposed to as a source of inborn vulnerability to aging dis

eases). This is because mutations only spread from one cell to another

when the second cell's DNA is actually derived from the DNA of the first,

as happens when (and only when) a cell divides and passes a copy of its

DNA on to its progeny. Thus, whereas inherited mutations infect all of the

cells in our mature bodies (because all of our mature cells derive from a sin

gle, mutated fertilized egg), age-related mutations happen in our mature

bodies one cell at a time, as a result of random events like the radiation that

comes into a plane at high altitude, or toxins produced by invisible mold

spores in your food. Any such mutations can only affect the one cell in

which they occur, and its descendents.

This fact greatly limits the potential of age-related mutations to become

prevalent enough in our tissues to impair function. A lot of our cells—

including the ones in tissues where the impact of aging is most clear, like

the brain and heart—don't divide at all once we mature, so any mutations

in such cells go no further. And even in cells that do divide—skin cells, say,

or the cells lining your gut—the rate of cell division after we mature is bal

anced by the short life of the cells' descendents, so that an individual cell's

mutations are present in only a few cells in the body at any instant and thus

get little chance to "take over" the tissue in which the mutation occurs.

Also, even before we had hard numbers on the subject, we knew that

complete "knockout" mutations would be relatively rare occurrences. For

one thing, most mutations in DNA create errors in the encoded proteins

that, if they affect proteins at all, only make them less effective, rather than

completely dysfunctional. But even in cases where a gene is damaged so

badly that either it can't be used as the basis for protein manufacture at all,

or else the product that it produces will be useless—or even toxic—still

generally no harm will ensue, because the damage will be to a gene that


isn't even being used in that cell! Remember that the DNA of each cell in

cludes not just the genes needed for that cell to do its specialised job, but

the entire instruction manual for producing every cell type in your body.

Individual cells acquire their specialized function—heart cell, liver cell,

kidney cell, skin—by turning off most of their DNA, leaving active only

those genes that they require to perform their particular function. In a typ

ical cell, only about one tenth of a person's full gene complement is active.

So about 90 percent of the genes in a cell could be irreparably damaged

without affecting the cell's function one bit.

It gets better yet. Even though evolution is far too thrifty to allow cells

to go around wasting their resources in producing proteins that aren't im

portant to cell function, the cell can nonetheless suffer the loss of many

proteins and still limp along without harming the body, even contributing

in some degree to its internal economy. Remember, many people are born

with such mutations affecting every single one of their cells, including all

the cells where that protein is normally needed to do their jobs, and these

people still live for decades. The same mutation occurring in only a small

fraction of one's cells might not even be noticed in a normal lifetime, being

compensated for by the fact that the rest of one's cells are fully functional.

Mutations: Few, and Not Far Between

And sure enough, the actual number of mutations that accumulate with ag

ing does indeed appear to be rather low—too low to have any serious effect

on the aging of the tissue in which they appear. We know this thanks in

large part to the work of a team headed by physiology professor Jan Vijg,

now at the Buck Institute for Age Research. Vijg's group came up with a

very ingenious way to obtain a representative sample of both the amount of

mutation that accumulates in different tissues with age, and the general

kind of damage that occurs.

What Vijg's group found was surprising to them and to a lot of other

researchers. They discovered, first, that there were not nearly enough rela

tively minor point mutations ("one-letter" mutations in DNA "words" or

"sentences") to realistically have a meaningful impact on overall tissue

function or on the aging of the organism as a whole.

More important, the number of mutations in a typical cell doesn't even

increase between early and late adulthood in our most critical tissue (the

brain), and the total burden of mutations only goes up by a factor of two to


three in any tissue, even in old age. 8 , 9 This may sound like a lot, until you

remember how many genes there are in such a cell and how few mutations

are present in young people. Doubling or tripling a small number of initial

mutations still leaves the cell with only a small number of them; and when

you consider how few of those are occurring in genes actually used by the

cell in which they occur, how few of that subset actually disable (as opposed

to merely inhibit) a critical function of the cell in question, and how little

the loss of a particular activity in a particular cell can really affect the over-

all function of a tissue, an organ, or an entire animal, it becomes clear that

an increase like this is actually more of an inconvenience than a crippling

blow to the aging organism.

But Vijg immediately appreciated that this was not a knockout blow

to the involvement of nuclear mutations in aging. This is because some of

the mutations identified by his group may be much more severe than the

disabling of a single gene. Some of them, for instance, could take the form

of deletions—the total removal of large stretches of DNA, annihilating

many genes at once even though the event is, strictly speaking, only a sin

gle mutational event. Deletions can occur when two widely separated

breaks occur at the same time in the same chromosome, and Vijg's data

showed that a significant proportion of the mutations that accumulate

with age do involve such breaks, which at first glance suggests there are a

significant number of deletions amongst the modest increase in the total

number of mutations that happens with aging. This would have a much

greater impact than would be suggested by a simple tallying-up of muta

tion frequencies.

Luckily, however, it turns out that most of the cases in which a cell suf

fers two distinct breakages of DNA don't actually lead to deletions. 1 0 Fully

half of them are actually cases of fractures happening on two separate chro

mosomes, which are not physically linked to one another and thus do not

lead to a deletion—much as if you cut two separate pieces of string across

their respective middles and switch the pieces' partners, rather than mak

ing two snips in the same length of material and discarding the portion be

tween the two cuts. And even in the remaining cases, where both breaks

occur on the same chromosome, many of the incidents are equally harm

less, leading to mutations called inversions that shuffle chromosomes

around while typically leaving them intact and functional.

For this and other reasons, not many of the events that at first look like

deletions actually seem likely to have much more effect on actual genetic in

tegrity than simple point mutations.


When we look at epimutations, the evidence available so far leads me

to the same conclusion. The most well-studied kind of epimutation is

changes in methylation—a chemical alteration of genes that prevents them

from being expressed. Middle-aged mice 1 1 and humans 1 2 have indeed been

found to have more alterations in their methylation patterns than immature

ones do, but it's not clear that that trend continues further as the organism

actually ages (as would be required of a true, stable form of molecular ag

ing damage). Instead, as they go from adulthood into true old age, the

change in methylation epimutation may stop accelerating and may even

slow down. This could mean, for instance, that the observed methylation

changes occur in the early life of the organism, but that their frequency is

subsequently held to tolerable levels by repair mechanisms or even by the

elimination of unacceptably aberrant cells, rather than accumulating with

age the way that AGE cross-links or mitochondrial mutations do. Just as

important, from our perspective as would-be interveners, there's no evi

dence that the observed methylation changes cause any actual functional

problem over the life span.

Add it all up, and there seems to be remarkably little increase in muta

tions happening in aging cells—and of what there is, again, very few will ac

tually affect the cell's functionality.

The Times, Not the Genes, They Are A-Changin'

Vijg's studies of that period, and those of a few of his forerunners, assessed

the impact of mutations on aging by measuring the actual frequency at

which genes are structurally altered during aging. But there's another kind

of evidence that's often invoked to support the role of mutations in aging:

gene expression studies. Starting in the late 1990s, scientists were able to

use a new technology informally known as "gene chips" to measure the ac

tivity, rather than the structure, of nearly all the genes in the cells of tissues.

This allowed for comparison studies of aging and younger animals—

including humans. 1 3

The results clearly showed that there are pretty substantial changes in

gene expression in the cells of aging animals. This result has often been mis

takenly thought to prove the importance of mutations in aging, because the

gene expression shifts were assumed to be the result of mutations in the genes

themselves. This idea was given some seeming support by evidence that the

changes in gene expression happened alongside markers of "pre-mutagenic"


free radical damage to genes—damage that can still be repaired as it stands,

but that can go on to become full-blown mutations if not repaired properly.

But there's a much easier explanation for these shifts, and that is the

very fact that gene expression does change—not just with aging, but all the

time. Your cells are in a state of continuous dynamic adaptation to their en

vironment, changing gene expression in response to new conditions at

every moment. Every time your body needs to respond to its environment,

the expression of genes involved in those responses is altered.

So as cells and tissues acquire aging damage that impairs their normal,

youthful function, the body adapts to the changed circumstances as best it

can. As oxidative stress climbs with the accumulation of cells that have

been taken over by mutant mitochondria, cells ramp up the activity of

genes that produce protective antioxidants and "heat shock" factors that

help to repair some of the ensuing damage to proteins. When the increase

in oxidative stress leads your arteries to become infiltrated with free-

radical-damaged LDL, the surrounding cells produce more inflammatory

factors to attract macrophages to clear the toxic stuff out. When your heart

stiffens as it becomes riddled with cross-linked proteins, the body pro

duces more "remodeling" enzymes that help to degrade the old tissue in

hopes of clearing the way for fresh, undamaged replacement material.

Additionally, changes in the cellular environment imposed by aging

can also interfere with normal gene expression. In some cases, such effects

are easily observed: for example, oxidative stress directly inhibits the ex

pression of some genes. But there are also more subtle effects afoot. For in

stance, you'll recall that free radicals, in addition to being produced as

simple side effects of metabolic forces, are also produced intentionally as

signaling molecules in various systems inside and outside cells. As free rad

ical levels climb in the aging organism's cells, the excessive oxidative stress

distorts these same signalling pathways, introducing "noise" into them.

This can in turn result in inappropriate metabolic and gene-expression

shifts as the cell responds wrongly to misheard, drowned-out, or counter

feit messages from (or superimposed on) the system.

And so on. The point is that the age-related shifts in gene expression

seen in studies of tissues are not the cause of aging, but are an adaptive (and

sometimes maladaptive) response to it. Changes in gene expression in cells

subjected to free radical attack can occur not because that attack has dam

aged the genes whose expression levels change, but because an increase in

oxidative stress requires the cell to change its metabolism to keep going in

face of the challenge.


Now, you may be thinking that I've jumped the gun here. So far, I've

explained how gene expression changes can be a compensatory response to

aging rather than a cause of aging—but surely I have not shown that those

changes are, overwhelmingly, responses and not causes. But it's easy to see

that they must be responses, because they're coordinated. The only reason

the studies I'm referring to were able to detect a change in expression of a

given gene was because it was occurring in the bulk of the cells within the

tissue being analyzed. Mutations and epimutations, by contrast, would af

fect one gene in one cell and a different gene in the next cell.

This coordinated change of gene expression in response to aging is

shown most clearly in gene-chip studies that compare normally aging animals

to those undergoing calorie restriction ( C R ) , 1 4 , 1 5 , 1 6 which is, again, the only

intervention now at our disposal that slows down aging in mammals, short of

tinkering with their genes. These studies show that the greatest number of

changes in gene expression that happen with aging occur in the blueprints

for antioxidant, inflammatory, remodelling, and heat shock proteins—

exactly the ones needed to respond to the damage inflicted by aging. They

also show that CR not only slows down, but reverses, many of these changes

when it's implemented late in life. This shows that the changes in gene ex

pression can't be the result of mutations, because while CR can slow down

the accumulation of mutations and other aging damage, it cannot undo dam

age that has already been done. Rather, it reduces the sources of damage that

are leading to the changes in gene expression, cutting down free radical pro

duction in the mitochondria, reducing the accumulation of mitochondrially

mutant cells, lowering blood glucose to prevent glycation cross-links, and so

forth. Change the cells' pro-aging environment, and they scale back their

gene-expression adaptations to that environment.

This sort of logic has led some, among whom Vijg's team are again

prominent, to conduct much trickier studies assessing the variation of gene

expression from one cell to the next in old animals as compared with young

ones It was found that there is a dramatic increase with age in that varia

tion. 1 7 On the face of it, this increased variability doesn't seem likely to be

the result of the kinds of adaptation that are responsible for the dominant

pattern of age-related gene expression shifts that we were talking about a

moment ago, because the conditions that create them—and the adaptive re

sponses needed to keep going under their influence—are more or less the

same from one cell to the next in a given tissue.

But there are a lot of alternatives to explore before we jump to the con

clusion that this increase in the amount of difference in gene expression be-


tween a given aging cell and its neighbors is the result of mutations (or

epimutations). It may be due to some other age-related stressor, for in

stance. Vijg's team found that they could reproduce the increase in variabil

ity by exposing cells in culture to oxidative stress—and again, oxidative

stress disrupts the ability of cells to relay signals within themselves. Such

disruptions could lead to a failure to respond to signals coming in from the

cell's environment—either local signaling molecules from its neighbors, or

more "broadcast" signals like hormones and other factors. The effect of

this would naturally vary from one cell to the next, because it results from

noise in intra- and intercellular signaling, but if the oxidative stress were

then removed, the variability might return to its original level.

Variability from one cell to the next can also result from other kinds of

damage that have accumulated, randomly, to different degrees from one

cell to another: telomere loss in one cell, high levels of AGEs in another,

and the presence of mitochondrial mutations (without nuclear mutations)

in still a third. Intuitively, the gene expression shifts required to increase

the degradation of AGE-ridden proteins on the surface of heart muscle

cells are quite distinct from those that occur in response to accumulated

junk within them. When neighboring cells suffer different levels of differ

ent kinds of molecular damage, they mount different adaptive gene expres

sion responses, both to counterbalance the effect of the damage on their

ongoing metabolic processes and in many cases to attempt to repair it.

Such effects have been observed at the cellular level in roundworms, 1 8 and

preliminary studies suggest that similar factors could be at play in increases

in gene expression variability in rats and humans, too. 1 9

Also, such damage can send shock waves outside the cell in which it oc

curs, which will elicit changes in gene expression in nearby cells trying to

cope with its impact. Consider cell senescence, which I discussed in Chap

ter 10. The activation of the senescence program will certainly change the

expression of genes in the senescent cell as compared to its neighbors, but

it will also change the expression profile of those neighbors, as they re

spond to the flood of growth factors, inflammatory signals, and remodeling

proteins that it produces. Cells closer to the senescent one will be more af

fected than cells further away.

Importantly, these changes would distinguish the neighbors of a senes

cent cell both from the original culprit and from other cells not directly af

fected by its output. To pick the most obvious example: growth factors

secreted by a senescent cell will trigger cell-replication programs in nearby

cells. These programs, executed by gene expression changes, are ones that


have been permanently shut off in the senescent cell itself, and that are qui

escent in cells far enough removed from the senescent cell to evade its in

fluence.

The same would be true of cells that had suffered any number of prob

lems. And the variation can flow in the opposite direction, too. That is, in

addition to damaged cells playing havoc with their neighbors by exporting

their own internal woes, healthy cells can communicate with damaged ones

to keep them functioning more normally. The best-researched case of this is

cancer. 2 0 , 2 1 A single cell can harbor mutations that would by default lead to

malignancy, but be held in check by its neighbors, which can do everything

from inhibiting its proliferation (so-called contact inhibition) to inducing

apoptosis. As with all other adaptive changes, the output required to impose

this control requires shifts in gene expression that will distinguish cells work

ing to keep their antisocial neighbor under control from the patterns of both

the would-be cancer cell and noncancerous cells elsewhere in the tissue.

Hence, even the fact that there are more pronounced differences in the

activity of genes from one cell to the next in the tissue of old animals (as

compared with young) doesn't necessarily pin the blame on nuclear muta

tions. Moreover, much of the variability observed is a good thing—the dis

tinct efforts, futile though they may ultimately be, of each cell to preserve its

integrity under the unique burden of aging damage that each of them faces.

If, then, age-related gene expression changes don't flow out of a signif

icant increase in nuclear mutations, but are instead the result of other kinds

of damage (and cells' attempts, successful and otherwise, to carry on in the

face of it), the proper engineering response is to leave nuclear mutations

alone, and focus our attention on the real culprit in age-related gene dys-

regulation: the aging damage that forces our cells to flail about in increas

ingly desperate, disorderly, and panicked attempts to keep their heads

above the waters of the aging process. Once our cells are no longer suffer

ing under the onslaught of problems ranging from mitochondrial mutations

to AGE cross-linking to visceral fat accumulation, their gene expression

profiles can be expected to normalize, because both they and their environ

ment will be normalized—returned to a youthful state of functionality.

Ironically, it may be precisely after we have cleaned up all of these

sources of damage that nuclear DNA mutations may, eventually, begin to

contribute to age-related death. The evidence shows only that cells accumu

late relatively few nuclear DNA mutations, and those mutations do relatively

little to impede cell function within a normal lifetime. But what happens

when that life span is extended to centuries, with the same amount of meta-


bolic damage to our DNA occurring, and with our DNA-replicating and

DNA-repairing machinery no more perfect than it is today? It may wed be

that effects that are too subtle ever to reach a pathological stage within nine

decades or so could build up into a real threat over the longer term.

However, we don't need to worry about that now. As I explained in re

spect of AGE cross-links in Chapter 9, one cornerstone of the engineering

approach to developing anti-aging biotechnology is that we don't need to

fix all possible forms of damage at once—we only need to do a good

enough job of cleaning up those insults that meaningfully contribute to

age-related frailty within today's life expectancies. Once this is accom

plished, our bodies will remain youthful during the years in which they are

now undergoing a slow descent into decrepitude. Some forms of molecular

damage that aren't causing us problems now will then begin to reach the

threshold beyond which we begin to meaningfully, functionally decay.

At that point, the next generation of SENS therapies will need to be

brought in, to repair that newly pathological (and in some cases even newly

identified) damage to the same standard. Fortunately, our extended lives

will buy us the time to observe such damage accumulating in our bodies,

and in those of shorter-lived animals whose lives have been extended in the

lab, and whose youths renewed, using the same treatment—and as time

goes by, we'd build better and better tools for identifying that new damage

and for developing weapons to fight it. The key is to get past the barriers

that hold us back today, and then be ready to break new ones as they ap

proach. From all available evidence, nuclear mutations aren't yet such a

limit—but they may well be one in the future.

The Exception That Creates the Rule

So far in this chapter, I've explained that one of the reasons not to worry

too much about nuclear DNA mutations is that even the ones that are actually harmful to the cell are usually minor and, even when they are major, the

damage that they inflict is mostly constrained to one or a few cells, so that

any slack that their dysfunction creates can be picked up by other cells in

the tissue. But there is, of course, one screamingly important exception to

this rule: cancer. Cancer is famously a disease of nuclear DNA mutations

(though, as we've seen, it usually takes more than just mutations to turn an

aberrant cell into full-blown cancer). And the incidence of cancer clearly

goes up with age.


Shortly, I'll discuss how I think we can really defeat cancer. But first,

I'm going to explain why cancer is the reason for our apparently "unneces

sarily" good defenses against the accumulation of nuclear mutations.

First, let's recall that one of the reasons cancer is so formidable an ad

versary is that any number of different mutations can contribute to the can

cer process. A breakdown in any one of the many systems that protect

against cancer—mutations that lead to the formation of a defective senes

cence or apoptosis "tumor suppressor" protein, or to the excessive produc

tion of a cell receptor for growth signals, or to the reactivation of a

suppressed telomerase-coding gene—can be a key step along the broad

and winding road that leads a healthy cell to become a renegade.

As with all other causes of age-related death, the evolved level of pro

tection against potentially cancer-causing mutations is limited by the cost of

creating and maintaining the machinery to achieve that protection. On the

one hand, there's no sense in putting all of an organism's eggs into the bas

ket of being so resistant to aging processes that it can stay young and

healthy for two hundred years, if there are strong odds that it will freeze,

starve, sicken, or become something's lunch in its third decade; those re

sources would be better spent on warmer fur, sharper claws, or simply a

shorter gestational period. But on the other hand, the animal does need to

remain internally intact for as long as it can reasonably be expected to sur

vive those threats from the external environment, because every year of

youth is another opportunity to spread one's genes around. If you're unsure

about this, go back and reread Chapter 3.

Given those opposing priorities, natural selection will push hard to

create machinery that protects against potentially cancerous mutations rig

orously enough to keep cancer at bay for at least as long as the organism

would likely get through winters, wars, and attacks from predators. But,

precisely because of the nature of the cancer threat—that so many alterna

tive mutations can contribute to the cancer—the body can't afford to

cherry-pick the genes that it's going to protect. The only effective defense

against cancer is to safeguard the integrity of every single gene we possess.

So this is how it comes to be that new, age-related nuclear mutations

are so rare—why we possess such an elaborate system of oversight of DNA

synthesis repair guarding our every gene, despite the fact that the great ma

jority of mutations have negligible effect on the overall economy of the

body. To protect the organism adequately against cancer, evolution gets the

best bang for its buck from a system in which every gene gets the kind of


gold-plated antimutation defense that you might think it would reserve for

a privileged few, mission-critical, cancer-avoidance genes . 2 2 , 2 3

A 2015 Challenge

This analysis shows that we don't need to address all mutations in order to

develop a panel of interventions comprehensive enough to result in the first

dramatic extensions of human life span. My realization of this was crucial

to the nascent development of the SENS platform back in 2000, because it

showed me that the sheer scope of the nuclear mutation problem was in

one sense much smaller than I had at first feared. It had become clear to me

that, for the most part, age-related accumulation of nuclear mutations are

basically harmless over the course of a currently normal lifespan: the rate of

their accumulation is quite insufficient to contribute significantly to age-

related decline. But we emphatically do need to confront the one enormous

exception to that rule: cancer. In principle, we can simply ignore nuclear

mutations, if and only if we can find a truly effective way to protect our

selves against this one fatal disease.

The stakes here are high. Cancer is a deal-breaker for building an age

less organism. We can shatter the cellular manacles of AGE, free our brains

and hearts of the webs of amyloid, clean out the dirty depths of our lyso

somes, and all the rest—but if we fad to make a breakthrough against this

one disease, we can still expect to be dead in our mid-eighties.

If you've been listening to the popular press accounts of progress in the

War on Cancer, you may now be feeling much less alarmed than you

should. The media, and also the scientists and bureaucrats on whom they

report, love to trumpet every advance (indeed, every hint of an advance) in

the treatment of cancer. There are so many reports of potential new cancer

treatments that one might well think we were already far down the path to

the day when we will have cancer mastered. This is especially so in light of

the targeted cancer therapies that I reviewed in Chapter 10—therapies that

generally are, or can be predicted to be, far safer and more effective than

the knives, poisons, and radiation that have been the staples of cancer man

agement for decades.

And you wouldn't be alone, nor even outside the scientific mainstream,

in thinking this. In 2003, none other than Dr. Andrew von Eschenbach, the

Director of the National Cancer Institute, famously put forward an ambitious


but (so he claimed) realistic vision for his organization: to eliminate suffering

and death from cancer by the year 2015. Dr. von Eschenbach wasn't just

whimsically putting his dreams into words: he was putting forward his sober

assessment of what the world scientific community, spearheaded by the NCI,

could achieve in little over a decade. It became the formal agenda of the In

stitute: "Challenge Goal 2015." The timetable is now so embedded in the or

ganization that it is routinely alluded to as simply "2015," with no further

elaboration necessary—in the same way that we once talked about "Y2K." 2 4

I think that this goal is utterly unrealistic—and that it only arose be

cause of a failure to appreciate the flaws in the assumptions that are built

into it. First, and quite explicitly, "it does not mean 'curing' cancer but,

rather, it means that we will eliminate many cancers and control the others,

so that people can live with—not die from—cancer."2 5 If feasible, this is a

perfectly legitimate medical goal: to have cancer under the same level of

control that we today have over adult-onset diabetes or AIDS—in which

the disease is still present but is so well managed that patients can lead

nearly normal lives—would represent an enormous alleviation of human

suffering and death from a terrible disease.

But cancer is fundamentally different from these diseases in a way that

precludes its chronic "management." Diabetes and hypertension can be

held at a safe, manageable level precisely because they are essentially stable

diseases. By contrast, what makes cancer so fearsome a foe is that it's a con

stantly evolving disease, a hive of genetic inventiveness that continuously

finds new and better ways to outwit our attempts to control it. Relegating

cancer to the level of a chronic disease is an idea that could only ever be en

tertained by completely ignoring the basics of natural selection.

Cancer cells are characterized by an immense genetic instability, which

results in large part from the fact that they nearly all get started from a mu

tation in one or more of the "guardians of the genome"—the genes that po

lice mutations and direct either repair of DNA damage or the activation of

senescence and apoptosis programs. Without this constant surveillance and

maintenance, the random damage that cells suffer every day is allowed to

develop into full-blown mutations, and the process feeds on itself as more

regulatory genes are lost.

Many of these mutations are fatal to the cancer cell, but a few of them

result in viable progeny that are just different from their parents and half-

siblings. And that's where natural selection comes into play. Cancer cells,

by definition, are reproducing themselves at an astonishing pace. They

throw their bastard children out into the world and let survival of the fittest


reign. The immune system or oncologists soon take their best shots at the

tumor, exploiting the soft spots in the cancer cells' metabolism: their re

liance on particular growth factors, for example, or their need for a reacti

vated telomerase gene, or their hunger for folic acid. But within a single

tumor exists such an astonishingly varied population of cells, each with its

own combination of normal and abnormal genes, that at least some of those

cells nearly always have a way to survive any particular attack: a greater abil

ity to detoxify a particular toxin, or an alternative way to keep their growth

fueled even when a particular signal transduction pathway is shut down.

As a result, it ultimately just doesn't matter if a given therapy kids 99

percent of the cells in a tumor. Somewhere within its heart lurks the dark fa

ther of a "strain" of the cancer with a novel mutation that allows it to survive

the drug that destroyed its cousins. This founding cell's furious growth con

tinues even as we decimate its cousins, or resumes when the patient can no

longer tolerate the stresses of the treatment. Its descendents remain standing

after the assault, and are thereby selected for survival by the very thing that

killed their cousins. When the ensuing tumor becomes large enough for us to

detect, we attack what seems to be the same cancer in the same patient using

the same treatment, but this time, the old tricks don't work. There really is

plenty of truth in the saying that you can't outsmart evolution.

As I sat reflecting on all of this in the wake of my original SENS "Eu

reka! " moment at the turn of the millennium, a grim formulation of the prob

lem crystallized in my mind. It is not my goal, I thought, to buy time for cancer.

Making Cancer Wilt Away

Soberly, I contemplated my own cancer challenge: to develop a cancer

treatment that would keep us free of clinical cancer for just as long as the

other SENS therapies would keep us free of other age-related maladies.

The reasoning outlined above immediately ruled out all existing ap

proaches, which leave us fighting one battle after another against an enemy

with the implacable force of evolution on its side—a war in which we can

win individual campaigns but must ultimately be defeated.

The answer came to me in March 2002 while nursing a beer in a cafe in

Italy. As my mind had done late that night in California in 2000, it now leapt

upon an insight that was in some ways completely obvious, and yet led inex

orably to revolutionary conclusions. To defeat cancer, I saw, we would need

a therapy that does not depend on anything that a cancer could escape


through a mutation-driven change in gene expression. So any solution

would have to have three key characteristics to be viable. First, it would nec

essarily involve denying cancerous cells access to some tool that is absolutely

indispensable to any cancer's survival, so that they couldn't just make up for

its loss by tweaking some other gene expression pathway through mutating

its other genes. Second, we would have to take away that tool in such a way

that no mutation could restore it, either. And third, this tool would have to

be one that our normal, noncancer tissues could do without.

I quickly saw the tool that I wanted to lock up: telomerase. I mentioned

this enzyme back in Chapter 10, when discussing senescent cells; now's the

time to explore it in more detail. Our DNA comes equipped with a stretch

of nonsense or "noise" DNA called the telomere. Telomeres are to our

genes as the brief, silent stretch of "leader tape" at the beginning of a music

cassette is to the songs on the tape: they give the "cassette player" (the

DNA-replicating machinery) something to hold on to and advance over, so

that it won't skip over the essential information at the beginning of the very

first "song" (gene) on the tape.

One key difference between telomeres and cassette leaders is that lead

ers stay intact as long as the tape does, whereas telomeres become ever-so-

slightly shorter every time the cell replicates itself or is hit by damaging

agents like free radicals. If it weren't for telomerase, this gradual shortening

would eventually lead to the complete loss of the telomeres in cells that

replicate frequently during the lifespan, and thus the gradual erosion of the

genes themselves. Telomerase periodically relengthens the telomere before

it becomes critically short.

As with all of our other genes, the DNA that encodes the telomerase

enzyme is present in all of our cells—but, because it's only needed after

quite a few cell divisions have occurred, it's not needed in most cells for

most or all of the time, so it's turned off. This widespread lack of the need

for telomerase is used by evolution as a key component of our defense

against cancer, because having a limit to the size and renewal of our telom

eres prevents our cells from replicating themselves indefinitely—the crucial

hallmark of cancer.

To become a full-blown cancer (as opposed to a cell with a single, po

tentially threatening mutation—a genetic risk factor for becoming a cancer)

requires the accumulation of five to ten mutations, and statistically that re

quires multiple rounds of cell division and selection. The arithmetic is com

plex, but the consensus is that, to pose a health threat, cancers have to

replicate at least two to three hundred times, even though a clinically rele-


vant tumor contains "only" a million million (a " 1 " with twelve zeroes after

it) cells, which could be achieved by "only" forty or so divisions if the orig

inating cell had all the necessary mutations from the outset. And to be gen

uinely malignant (i.e., to be the founder of a colony of cancer cells that

spreads its way throughout the body, as opposed to a localised tumor that

could be simply removed with surgery and forgotten about), cancers must

then be able to keep up the feverish pace of their replication even longer.

The frenzied reproduction of cancer cells is also a key part of their ability to

evade our assaults, because it is essential to their capacity to evolve new so

lutions to the challenges that we throw up against them.

It's no surprise, then, that mutations that unleash telomerase from the re

pressive strictures imposed on it in normal cells are found in over 90 percent

of cancers. The remaining 10 percent also have a way to renew their

telomeres—a little-understood mechanism called the "Alternative Lengthen

ing of Telomeres" (ALT) pathway, which I'd discuss a little later on. Either

way, without a way to renew their telomeres, the single-minded multiplication

of potential cancer cells rapidly grinds to a halt as it reaches the end of its

telomere "rope," and we wind up with a tiny (and generally short-lived) lump

in our bodies instead of a life-threatening, malignant disease.

If, then, we could snatch this one tool out of the hands of cancers, we

would cause any and all the aspiring cancers we developed to fizzle out be

fore they became life-threatening—indeed, before many of them even be

came actual cancers, because they wouldn't get the opportunity to undergo

the full spectrum of mutational events needed to give rise to the kind of

renegade cell that can truly pose a threat to the body.

Of course, I was hardly the first to think the problem this far through.

Several biotech companies—most prominently Geron, which first made a

name for itself in telomere research—are working to develop anticancer

drugs that would work by deactivating telomerase. But these pharmaceuti

cals suffer the same problem as all other approaches based on drugs that af

fect gene expression: they act as a force of natural selection against a

disease with evolution at its disposal. A telomerase inhibitor would kill off

those cancer cells in which it effectively turns off the enzyme (and in which

ALT didn't take telomerase's place), but it would leave behind any cells that

harbored mutations allowing them to keep on renewing their telomeres in

the face of it. Different cancer cells might bear any number of variations

that let them escape the drug's effects. Some would simply crank their

telomerase activity up even further; some would enhance the activity of

drug-metabolizing enzymes that degrade the inhibitor; still others would


change their cell surface proteins in ways that would make it harder for the

drug to penetrate into the cell. Whatever the mechanism, if even one can

cer cell can evade the effects of such a drug, it can act as the seed for the tu

mor's renewed blossoming in a dark spring.

So, again, there was no sense in doing the job only halfway. If we're go

ing to snatch telomerase out of the hands of cancer cells, I thought, we must

really take it away. And there was only one way that I could think to do that

reliably: by deleting the gene that encodes it.

Evolution can, of course, create whole new genes—but it takes a very,

very long time to do it. Indeed, very little evolutionary change actually in

volves the creation of new genes, or even the removal of old ones, precisely

because it's so hard to do: instead, evolution finds new ways to regulate old

genes, or new functions for gene products other than the ones for which

they originally evolved. 2 6 Thus, for example, the lens of the eye is made up

of clear, flexible proteins called crystallins, which would seem to have no

purpose other than to be used to focus light. Yet, there it is in the nervous

system of the sea squirt, where it is part of an organ that keeps track of

"down" by sensing gravity. The gene is of course present in every cell in its

body, and a mutation in a proto-eye cell of one of our ancestors that carried

this gene may have caused it to be expressed there, where previously it

would have been turned off, making the protein available to let the light

shine on in. And our genome contains no genes similar to the ones for

telomerase, ready to mutate to replace it on cancer's demand.

So deleting the telomerase gene, unlike trying to inhibit it somehow,

would be an almost sure-fire way to shut down cancer cells permanently.

(Again: this logic ignores Alternative Lengthening of Telomeres but fear

not—I will get to ALT shortly.) I had hoped back in 2000, and even specu

lated in the paper arising from the first SENS workshop, 2 7 that there might

be some way that we could do this only in cancer cells. I became increas

ingly aware, however, that while it might wed be possible to do this for most

cancer cells, we'd never be able to do it for all, for the same evolutionary

reasons that I keep hammering on: any mechanism that targeted cancer

cells exclusively would have to have some mechanism for selecting a differ

ence between them and normal cells—and of course, those differences

would have a genetic basis, leaving the flap of the "tent" open for a mutant

subpopulation of cancer cells to stick its evolutionary "nose" under.

Finally, fully eighteen months later in that Italian cafe, I stopped trying

to run from this conclusion. The only way to be sure that we were denying

telomerase to cancer cells would be to deny it to all cells. What we needed,


I realized, was to take the telomerase gene out of every cell in the body,

along with the ALT mechanism whereby a small minority of cancer cells

manage to lengthen their telomeres without relying on telomerase itself. I

would soon term this therapeutic target the "Whole-body Interdiction of

Lengthening of Telomeres" (WILT).

Removing telomerase from every cell in our body would preempt can

cer before it got a chance to get started. But you can surely see why I took

so long to explore this option—and why no one else had explored it before

me. Deleting telomere elongation capacity throughout the body would also

be life-threatening, because it would mean that our regular, proliferating

cells (like those in the skin or the lining of the gut) would suddenly have

iron limits on their ability to reproduce themselves and thus replenish tis

sue. From the moment that we denuded our cells of telomerase, a clock

would be ticking. With each division the telomere would shorten by a

notch from whatever it had been when we took telomerase out. We would

be under the specter of a rather horrible death, as our stem cells went off

line one by one under replicative senescence (see Chapter 10): with each

failure of a stem cell responsible for supplying key functions, the tissue

would fail to be renewed and would slowly degenerate.

So, the effect of telomerase deletion on frequently dividing cells would

indeed be very serious indeed—fatal, in fact, in what I calculated to be

around a decade from the point when telomerase was deleted.

But hang on, I immediately thought, SENS already has a proposed solu

tion to "normal," age-related cell loss: stem cells. So we might just be able to

deal with cell loss if we had a sufficiently sophisticated program of stem-

cell replenishment—using cells engineered to lack the one linchpin func

tion for cancer, namely telomere elongation.

Of course, these stem cells would eventually peter out, too, as their

telomeres were worn down—but this is just the same situation that we face

with all aging damage. The engineer knows that we don't have to root every

last trace of cellular and molecular injury out of our systems in order to

build a body that will not suffer age-related degeneration and death. The

tissues of a twenty-year-old are already riddled with aging damage, and the

level climbs every day, but you'd be hard-pressed to find much of a health

difference between a basically clean-living person at twenty-five and the

same person at thirty-five, because their level of damage at thirty-five is still

beneath the threshold at which it causes functional deficits. As long as we

keep it there, we will remain biologically young.

So if we introduced stem cells with nice, long telomeres in the first


place, we could let them wind down and eventually be lost to apoptosis,

senescence, or other sources of damage—and just top our tissues up with

more stem cells before enough of those cells were lost to begin to impair tis

sue function. The need for regular treatments in this case would, ultimately,

be no different from the need for regular rounds of AGE-breakers or of

purges of anergic T-cell clones. Neglect your medicine and you will eventu

ally suffer the consequences; keep up with your schedule, and stay young

and healthy into a boundless future.

In this case, the engineer's logic is even stronger, because the same

"damage" that might eventually kill us (in this case, the running down of

our telomeres) is simultaneously the very thing that we need to ensure does

happen, or else we will be killed by another means (the unchecked cell di

vision at the heart of cancer). Putting an expiry date on all of our cells, but

ensuring that they are regularly replenished with new ones, erases both

problems at once.

In fact, the case for deleting telomerase was even stronger than this, be

cause placing an absolute limit on the number of cell divisions that our stem

cells (and the mature cells derived from them) could undergo would actually

bring us an additional anticancer and anti-aging benefit. While we often are

given the impression that most age-related nuclear DNA mutations are the

result of damaging agents like free radicals, radiation, and mutagenic chem

icals, the reality is that most nuclear mutations are the result of errors made

in copying the DNA during cell division. And while it's almost never men

tioned in the popular press, most cancers arise not in the mature cells of our

bodies, but in our stem cells, where regular cell division and an active telom

erase gene makes it relatively easy to take the brakes off cell growth. 2 8 (It

was, in fact, precisely my increasing appreciation of this fact during 2001

that forced me along the line of thinking that led to the WILT concept.) By

cutting down on the number of divisions that our stem cells can undergo be

fore they die, we would simultaneously reduce the number of mutations that

they would ever accumulate—and thus, the risk that they might suffer the

combination of mutations that would turn them cancerous.

At that point, we'd have cancer licked. No cancer could reach a clini

cally significant stage. At worst, we would end up with a few little pebble-

tumors, small bads of abnormal cells that have exhausted their ability to

grow, no more life-threatening than a mole or a small cyst. And our normal

tissues would be preserved intact, provided that we underwent regular

rounds of replacement of stem cells. See Figure 1.


Figure 1. The effects of traditional (late-acting) cancer therapies (b), telomerase deletion (c), and telomerase deletion plus stem cell reseeding (d) on the prognosis for cancer (a).

- * P So Crazy, I t Just Might Work

I will not conceal that, when they first hear about it, virtually all my col

leagues think the WILT proposal is utterly mad. Indeed, I myself, while not

doubting my own sanity, initially worried that I must surely be missing

some life-threatening side effect of the two-in-one intervention that was be

ginning to firm itself up in my mind. So I began consulting experts in all of

the relevant fields—telomere biology, mutant humans, mice lacking func

tional telomerase genes, the ALT mechanism, stem cells, bone marrow

transplantation, and of course cancer as a disease above and beyond its

characteristic preservation of its telomeres—to confirm that I had my facts

straight and hadn't neglected any actual showstoppers, and to ask them


what they thought of the technical challenges facing the development of

each of the biotechnologies that would be required to implement it.

Their reaction was interesting, and typical of my experience in net

working with experts from different fields on interdisciplinary projects.

Presented with the whole scheme, each of these experts thought the project

as a whole was audacious at best, and something straight out of "soft" sci

ence fiction at worst. But to my moderate surprise, when I asked each of

them to assess the feasibility and timescales for the development of the in

dividual components that WILT would take from their own discipline,

each and every one thought them achievable (albeit ambitious), and felt

that nothing in the subfield of biomedicine in which they worked every day

would pose an insurmountable challenge. It was in the areas that they

didn't have intimate, working familiarity with the science or the biotechnol

ogy involved that they made assumptions of intractability.

Encouraged by these discussions, I held the third SENS workshop

specifically on WILT, inviting many of the experts I'd already been con

sulting about the field. As with the 2000 meeting, my purpose was to put

the participants in a room together and simultaneously put them to work

fleshing out the way forward (or else the proof that none existed) to the

complete, integrated intervention, thus showing them (I hoped) that the

plan was sound in its elements and as a whole.

To my enormous satisfaction, it achieved both ends, and we published

the results together in the Annals of the New York Academy of Sc iences .

And of all the experts that were involved in the roundtable, only one scien

tist objected to being given the credit (and blame) for authorship of the

paper—and her reasons were extremely revealing, as the Acknowledge

ments section of the paper, written with her approval, indicates. Dr. Nicola

Royle, senior lecturer at the University of Leicester's Department of Gene

tics and an expert on telomeres (and especially the ALT mechanism), in

sisted that her name be withdrawn from its author list, not because she

didn't think that WILT would work, but because she very much feared that

it would. Her concern was that, as far as she could see, there was nothing

stopping us from developing WILT as a final cure for cancer, and especially

as part of a complete panel of SENS interventions that would finally free

humanity from age-related degeneration, leading to indefinite youthful,

healthy lifespans. But she was not ready to embrace that future: like so

many others, her principled (but, I of course maintain, misplaced) fear

about the potential drawbacks of unbounded human lifespans on the envi

ronment and on existing social structures was so great that she wanted no


further part in promoting our progress toward any part of the SENS

agenda. 3 0

Let's look at some of the technical challenges and concerns that were

discussed at this SENS roundtable—and, of course, in follow-ups with

these scientists and other colleagues at other venues ever since. 3 1

What Happens When We Take Telomerase Away?

This is an obvious one. We're talking about taking away a gene that is at

least present in all of our cells, though it's permanently turned off in tissues

where the cells never have to divide, like the muscles, the heart, and the

brain. At least on the face of it, we wouldn't think that taking the gene (ei

ther or both of two genes in fact, as telomerase has two subunits) right out

of the cell would cause these cells any problems. On the other hand, the en

zyme is expressed and routinely used (under strict controls) by cells that

need to undergo regular division—most notably stem cells. What would be

the effects of taking it away from every last one of them?

Fortunately, we have some pretty reliable evidence on this point,

thanks to two models: mice that have been genetically engineered to lack

one or other of the two subcomponents of the telomerase enzyme, and a

human inherited disease called dyskeratosis congenita (DKC). The picture

here, overall, is a pretty optimistic one.

Unlike humans, mice are born with telomeres long enough to last

them their whole lives without telomerase. (This makes mice a rather

tricky species to use as models for human cancer, in fact.) Therefore, mice

with their telomerase genes deleted have to pass their progressively short

ening telomeres on through several successive generations before much of

anything bad occurs. At that point, they develop the symptoms that you'd

expect from a lack of stem cells, which appear first in the tissues that mul

tiply the most. They become sterile as their sperm-forming cells run out of

steam, and their guts and skin start to become depleted of cells and fragile.

They also, ironically, start developing high levels of cancer, which

might at first seem to fly in the face of the entire program—but this is just

one of the ways in which mice are a fraught model for human cancer. First,

even though these mice telomeres are short enough to mess up stem cell

proliferation, they're still long enough to let cancers grow to a size that's

dangerous for a mouse, simply because mice's small size allows tumors

that would be harmlessly small in a human to impede organ function and


siphon off a fatally high percentage of their tiny bodies' resources. Second,

mouse cells find it relatively easy to activate ALT, so the fact that these

mice lack functional telomerase doesn't guarantee that they can't lengthen

those telomeres anyway. Clever combinations of telomerase deletion with

other mutations can largely sidestep these differences between mice and

humans, though, and when this has been done, 3 2 , 3 3 cancer risk went down

dramatically—in one case, to such low levels that none of the telomerase-

lacking mice had died of the disease at a point when all of the animals

from the same strain but with functional telomerase had been consumed.

DKC patients also give us reason for hope in the midst of their despair.

They have a variety of mutations that prevent the effective functioning of

their telomerase enzymes—either in telomerase itself, or in genes encoding

proteins needed for its normal working. Patients do hold on to some lim

ited telomerase activity, however. The likely reason we never see people

completely lacking in the gene is that humans have to undergo a lot more

cell division in the womb than mice do (and have shorter telomeres than

mice at conception), so fetuses with a more severe telomerase mutation are

probably aborted.

But telomerase activity in DKC patients is certainly very low. As a re

sult, their telomeres are shorter than normal folks', and they develop pre

dictable symptoms similar to those suffered by telomeraseless mice:

mottled or web-patterned skin; patches of abnormal, thickened white cells

in the mucous membranes, similar to those often seen in lifetime smokers;

weak, thin nails with ridges and fissures; hair loss and lung problems; and

bone marrow failure, causing problems with immunity, blood clotting, and

delivery of oxygen and iron to their tissues. 3 4

It used to be thought that the worst symptoms of DKC usually occur in

people in their teens and twenties, but we now know that it isn't quite that

simple—and the reason why that's so turns out to be very important. Dr.

Inderjeet Dokal, who works extensively with DKC patients at the Depart

ment of Haematology at Imperial College in London, told me and the other

participants back in 2002 at the WILT summit that he had noted that first-

generation DKC patients of a particular type, the ones that have a mutation

in one copy of a telomerase gene, don't develop symptoms until they're in

their forties—but that, as they pass on their preshortened telomeres to their

children and grandchildren, those that inherit the disease develop symp

toms earlier and earlier. He and colleagues later confirmed this preliminary

observation in rigorous studies of several families. 3 5 , 3 6

This fact reinforces the principle that it is not the lack of telomerase per


se, but the reaching of a threshold length by the telomeres themselves, that

causes symptoms. This is an optimistic finding, because it implies exactly

what we would expect (and hope) would be the case: that if we can period-

ically replenish the bone marrow and other stem cell pools with new stem

cells whose telomeres are wed above the critical length, we should be able

both to cure DKC and also to avoid all the problems of the disease in peo

ple with intentionally extinguished telomerase. Indeed, the best treatment

for DKC today is a bone marrow transplant, introducing new stem cells

taken from people without DKC to replace the ones that are being de

pleted.

What About This Periodic Stem Cell Replenishment?

T h e B o n e M a r r o w

Bone marrow transplants are, of course, already a common and nearly rou

tine procedure, not only for DKC sufferers, but also for patients with a

range of blood disorders, cancer patients who have lost their bone marrow

to radiation therapy, and many others. Still, there are many complications

in recipients today, and many technologies that we will absolutely have to

master if we are to use bone marrow transplants for WILT.

One reason why bone marrow transplants often don't "take" is that

they are not robustly incorporated into their niche in the bone while the

original stem cells are still there. For the first round of WILT bone marrow

replacement, we may have to perform chemotherapy to wipe out the native

cells—but we'd want to do this anyway to minimize the cancer risk of hav

ing those old, telomerase-competent cells left behind. In subsequent rounds,

the process will be easier, because we will intentionally wait to replace the

cells from the first round of transplantation until the cells introduced in the

previous round are beginning to die as their nonrenewing telomeres wear

down.

How often will this stem cell replenishment have to be performed? It's

looking good. People have done clever experiments to measure the average

time between divisions of blood stem cells, and it's at least a couple of

months in humans. Because it takes around fifty divisions before human

cells not expressing telomerase start to feel the shortness of their telomeres,

this rate of division should be slow enough to enable us to function just fine

for about a decade between successive rounds of bone marrow replacement.


T h e S k i n

Because of the pressure to supply skin grafts for burn patients, disfigured

children, and cosmetic surgery, we've made remarkably fast progress in

mastering the art of making new skin from stem cells. In mice, we can now

peel the skin right down to the dermis (the layer of tissue beneath what we

normally think of as "skin," which houses hair follicles, sweat and skin oil-

secreting glands, and blood vessels), and fully reconstitute the old skin that

we've removed. The cells of the dermis do not divide regularly, so we don't

need to worry about their telomeres running out. Remarkably, the epider

mis (the layer on top of the dermis, which is where we do need to replace

stem cells) can be replaced using stem cells derived even from such differ-

ent locations as the cornea of the eye, and the dermis orchestrates their

rapid transformation into hair follicle stem cells that then expand outward,

renewing the tissue.

Again based on how often skin stem cells divide under the status quo,

a round of skin stem cell replacement should last us about ten years. Be

cause the skin is so easy to access, it should be among the easiest and least

invasive of WILT stem cell replacement routines. *

T h e L u n g s

The innermost layer of the lung, like the skin and the gut, is continuously

sloughed off and is thus in continuous need of renewal. Unsurprisingly,

lung complications are a major cause of death in DKC patients. Because

the lung is in important ways similar to the skin, and is relatively easy to ac

cess, there is no reason to think that we won't make quick and relatively

painless progress on this front once we put our mind to it. Indeed, some sci

entists are doing this already, mostly in hopes of treating cystic fibrosis pa

tients. Better yet, the latest estimates are that lung stem cells divide

considerably less often than even those in the skin.

Work to date has gone forward using similar approaches to those used

in skin, though not yet from stem cells. Even so, progress is being made. In

two different models of immunodeficient mice, scientists have purged the

lung of its "skin" (epithelium), "scraping" it down to the underlying base

ment membrane, and then replaced the lost tissue using restructured cells

taken from the innermost layer of the human lung. The next step will be to

do it with stem cells.


T h e G u t

So far, there are still significant challenges facing the replacement of stem

cells in the gastrointestinal tract in humans. Several years ago, Dr. F.

Charles Campbell, now Professor of Surgery at the Queen's University

Belfast's School of Medicine, made the first major advance. His team ex

tracted stem cells from mouse intestinal tissue, wiped out the cells from

small stretches of the colon, and then repopulated the tissue with stem

cells, which differentiated into all the appropriate cell types and made fully

functional new tissue. Progress has not been rapid since then, however. At

the WILT summit Campbell explained that, in studies he has never re

ported in print, his team tried the same approach in pigs, but the result was

a mass of dysfunctional scar tissue. Since then, however, considerable

progress has been made by another group working in dogs, 3 7 and the same

group has further advanced the technique in rats and mice.

Much work remains to be done here: not least, the opening-up of sec

tions of the gut to remove the existing cells would be far too invasive for

human use in WILT. Endoscopy, similar to what's currently in use to re

move potentially cancerous colon polyps, may provide us with a more tol

erable solution, and should be much more advanced in a few decades,

when we'll actually need it.

A further question is how often we will need to replace stem cells in the

gut. Previous estimates suggested that it would be much more frequently

than the decade or so needed in these other tissues—more like a few times

a year. Luckily, however, there is an easy way to see that those numbers

must be wrong. If gut stem cells divided so much faster than those in other

tissues, DKC sufferers and telomerase-lacking mice would suffer gut fail

ure at a younger age than they suffer failure of the bone marrow or skin—

but they generally don't. Rather, all these tissues fail at about the same age

in any given patient; if anything, the blood is most often the first to go in

humans, which is why bone marrow transplants are temporarily helpful.

But still, the replacement of the stem cells of the gut seems likely to be a

more invasive procedure than that in bone.

T h e R e s t o f U s

The rest of our bodies is, in the relevant respect, like the dermis: composed

of cells that don't divide regularly. Some of these cell types (including the

dermal cells, which are called fibroblasts) are quiescent: they can divide but


they only do so when called upon to do so, such as to close a wound. Oth

ers are postmitotic: totally unable to divide, and instead renewed by incom

ing progenitor cells, if at all.

Postmitotic cell types are obviously no problem in cancer terms, but

quiescent cells require a little more thought. The fact that they are not sig

nificantly affected in DKC or telomerase-knockout mice, and the relative

rarity of cancers derived from them, gives us a bit more time to work on

the job—and, once we have mastered it, probably a lot more time between

each round of stem cell reseeding (as opposed to the more targeted re

placement of "normal" and pathological cell loss to aging damage, which

we will be tackling earlier on using ESCs, as outlined in Chapter 11).

But, precisely because they don't divide, these cells aren't going any

where for a while either—and they do become cancerous occasionally.

Thus, we do want to protect ourselves from cancer in them as much as pos

sible. Removing senescent cells will reduce the already-low risk in these tis

sues considerably, but we will still want to cut it down much further.

The likely solution to this problem is targeted gene deletion. This is

again a major challenge, because even in mice (where gene therapy is now

routine) it's very difficult to target genes for insertion or deletion in cells

that are already inside the organism (as opposed to putting genes into

sperm or egg, or embryos, or into cells that have been taken out of the ani

mal, modified, and replaced). We are, however, getting better at this.

Hopes are high for using this technique for gene therapy generally, and it

could potentially be used to remove telomere-renewing potential from tis

sues that aren't maintained by stem cells.

Over time, however, between replacing age-related cell loss using stem

cells engineered to lack telomerase, and eventually replacing the original

stem cells for these tissues with new ones engineered the same way, we will

slowly "WILT-ify" these tissues a few cells at a time, progressively lowering

the cancer risk they may pose.

Does WILT Underestimate Cancer 's Evolutionary

Ingenuity?

WILT is a highly complex, multifaceted proposal—but it rests, as I've ex

plained, on one absolutely essential assumption. WILT will fail if cancers

can figure out a way to grow indefinitely without the genes that we delete.

Let's look at that eventuality in detail.


One formal possibility is that cells could develop a way to replicate their

chromosomes without telomere shortening, and thereby avoid the need for

any enzyme to reverse that shortening. It's been hypothesized that some stem

cells effectively do just this. When stem cells divide, they typically produce

one daughter that's still a stem cell and one "amplifying" cell that is set on the

path to differentiation into its required function. (Indeed, the ability to do

this is an essential feature of most people's definition of a stem cell.) It's pos

sible that, by a clever system of controlling which DNA strands stay in the

daughter stem cell and which ones go into the amplifying cell, stem cells

could stop their DNA from shortening. But we don't need to worry about

this possibility in respect of cancer, because it can only confer linear growth

rates, not the exponential growth that is seen in cancers. With linear growth,

a cancer would take thousands of years to grow large enough to kid us.

Another way to avoid telomere shortening is the way that bacteria, and

indeed our own mitochondria, do it: not to have any telomeres! Bacterial

and mitochondrial DNA are circles, so there's no end-replication problem.

But it seems that there's no meaningful risk of this happening in humans.

When telomeres get really short, the cell's DNA-repair machinery mistakes

the raw ends of the exposed chromosomes for the result of a chromosome

break. That causes the cell to make a misguided attempt at repair, joining

the chromosomes together, end to end—which is rapidly fatal for a dividing

cell, because the cell division machinery snaps the double chromosome

apart again, not at the original join but at some random place, scrambling

the genes into a dysfunctional mess.

The final possibility is altogether more real, unfortunately. I've men

tioned it a few times in passing during this chapter: it is that cancers can oc

casionally relengthen their telomeres using enzymes other than telomerase.

These enzymes have not yet been identified, so the system is given the un-

informative name ALT, or Alternative Lengthening of Telomeres. The good

news here is that ALT is quite rare—in some tissues it's almost never seen,

and in those few tissues where it does appear it occurs in no more than

about half of all tumors. This means that at least as much mutation is

needed to activate it as to activate telomerase—and that teds us that ALT is

almost certainly dependent on the turning-on of a gene that's usually very

firmly off, rather than only the loss of activity of genes that are normally on.

This is great news for WILT, because, if ALT is indeed dependent on the

activation of some gene or other, rather than just on the inactivation of

genes, we will be able to do the same for that gene (once we identify it) as

WILT proposes to do with telomerase. There may be side effects, just as


there are with deleting telomerase, but they should be addressable with

stem cell or other regenerative therapies, just as telomerase deletion seems

likely to be.

A S IDE E F F E C T : WILTING F E R T I L I T Y ?

One potential side effect of the loss of telomerase from all of

our cells might be eventual sterility for men. If having children is still

a priority in a post-rejuvenation world, then men may choose to

freeze their sperm in advance, as is presently done for sperm

donors, for IVF. The sole sexual issue will be the actual making of

babies, of course: nothing else will wilt from WILT.

Part Three

13

This book has presented, in as simple terms as possible, the biolog

ical details of what human aging is and how we can realistically set about de

feating it. However, from what I've presented so far, you would be entirely

justified in concluding that I've only made a case for the eventual develop

ment of therapies that could modestly delay aging. You might think that a re

alistic time frame for getting encouraging results in mice might indeed be a

decade or so, but you're probably already thinking about the problems that

there would be in negotiating FDA obstacles and such like in translating

these therapies to humans. And you may be concluding that the sort of time

frame I've been predicting for the arrival of widely-available therapies—a

few decades with 50 percent probability—is too short by a factor of at least

three. You're probably also pretty skeptical about the degree of life exten

sion that the techniques described in the last seven chapters could practi

cally achieve, even in that extended timeframe: sure, they might be truly

comprehensive if they worked absolutely perfectly, eliminating every scrap

of their respective type of target damage, but we all know that no therapy is

that perfect, and certainly not in its early versions. Thus, you're probably

thinking that I have fallen drastically short of making my well-publicized

case that a lot of people alive today may wed live to be one thousand—and

G e t t i n g f r o m H e r e t o T h e r e

T h e War o n A g i n g


you'd be absolutely right. Thus, in this chapter and the next I'm going to put

the scientific details to one side and directly address these two important

and legitimate concerns. I'm going to start with the time frame for wide

spread availability of the panel of therapies described in this book.

I use the phrase "the War on Aging" to describe a specific phase in the

process leading to the defeat of aging. I define it as the period beginning

with the destruction of the pro-aging trance and ending with the wide

spread availability of therapies that can add a few decades to the life span

of people who are already middle-aged. First I'll elaborate on this defini

tion, then I'll explain why I call it the war on aging, and finally I'll explain

why it has a good chance of lasting only fifteen to twenty years.

The pro-aging trance—the "rational irrationality" about aging that I

described and critiqued in Chapter 2—will end only when its claim to ra

tionality becomes unable to withstand even simple assaults, the sort that

most people can understand. I believe that this will truly occur only when

scientists obtain results in the laboratory—mainly with mice, I expect—

that are so impressive that the majority of professional biogerontologists

are finally prepared to say publicly that it's only a matter of time before we

can postpone aging by at least a few decades in humans. Science is in a very

real sense the new religion: what individual scientists say can be doubted,

but the public scientific consensus is gospel. The result that I think is

needed is something that I've called "robust mouse rejuvenation" or RMR.

RMR is a mouse life-extension result, and it's a rather precisely defined

one. That's what's needed if we want scientists to set aside their paranoia

about making predictions about what might happen in the future—we need

to close all the major loopholes. By my definition, RMR will be achieved

when:

at least twenty mice of the species Mus musculus,

from a strain whose natural average life span is at least three years,

receive treatments starting only when they are at least two years old,

and l i v e to an average of five years of age, with all the extra time be

ing healthy.

I thought about this definition pretty carefully before I publicized it,

and it seems to be standing the test of time: no one has pointed out any way

in which it could be achieved by "uninteresting" means, i.e., by means that

would not convince knowledgeable scientists that a massive breakthrough

had been made that was likely to be relevant to humans. The requirement

G E T T I N G F R O M H E R E T O - T H E R E 313

to use at least twenty mice is so that we can be sure the age wasn't a fluke or

a bookkeeping error. The requirement to use Mus musculus is because

other mouse species already live longer than Mus musculus but are less wed

characterised by scientists. The requirement to use a strain of that species

that naturally lives to three, which is unusually long for that species, is to

avoid any possibility that the mice have some specific congenital problem,

something that normally kills them rather young, and that the treatment

merely alleviates that defect rather than comprehensively affecting aging.

And of course the requirement that the treatment begin only when the mice

are already two-thirds of the way through their natural life span is to ensure

that it has potential relevance to people who are already alive, read the

newspapers, pay taxes—and vote.

My reason for calling the period that begins with the achievement of this

milestone the War on Aging arises from the initial, essentially immediate re

action that I expect society to have to it. In order to describe this reaction, I

must first describe a side effect of the pro-aging trance that determines soci

ety's current reluctance to take aging seriously. I have a name for this, too: it's

the triangular logjam. See Figure 1.

Experimental biology, like any other area of science, costs money—ready

quite a lot of money. Most biology isn't nearly as expensive as high-energy

physics or astronomy, but it's expensive enough that professors have to spend

Figure 1. The triangular logjam impeding funding, and how philanthropy can unlock it.


a hideous amount of their time fundraising. The overwhelming majority of

the funds that support experimental biology come from the public purse.

Biogerontology is typical in the above regard, but it's extremely un

usual in one way: the public are absolutely fascinated by it, so biogerontol

ogists get on the television all the time. I mean really, all the time. The

difference in this regard between biogerontology and other biological

fields—even really high-profile medical fields—cannot be overstated: even

quite junior biogerontologists get more press attention than the world's

leaders in other areas. And of course, when given that chance, biogerontol

ogists are just as keen as any other scientist would be to talk about their

own research—which, necessarily, is the research that they were able to ob

tain the funding to perform.

Consider, for a moment, what else a biogerontologist might choose to

talk about to the media. In particular, consider the possibility of talking about

research avenues that the public consider distinctly suspect: defeating aging,

for example. What are the attractions of discussing such topics? Wed, your

name might get quite widely known to the general public, and you might get

more media exposure. But hang on: What is the media exposure for? Scien

tists are intensely preoccupied, as I just mentioned, with the miserable busi

ness of maintaining a funding stream for their laboratories. How, exactly,

would a high media profile achieve this—or, conversely, make it harder?

In order to explain the answer to that question, I must make sure you

are aware of a key feature of the way in which public funding for science is

allocated. When scientists want to do a particular series of experiments,

they write a detailed description of what they want to do, how long they

think it'll take and how much it'll cost, and they send it to the appropriate

government agency. But the government agency doesn't then decide on its

own whether the scientist can have the money. No: even though such agen

cies employ highly experienced ex-scientists as administrators of grant

funds, those ex-scientists don't have anywhere near broad enough expert

ise to be able to tell the difference between a good idea and a poor one

across the whole range of scientific disciplines that they're responsible for.

So instead, they seek specialist advice from other scientists. This is called

"peer review" and it's an absolutely universal component of the process of

evaluating applications for government grants to do science.

Selection to evaluate your colleagues' ideas for experiments is an im

mense privilege and responsibility. It's not something that junior scientists

get to do very often; generally the most senior scientists are the ones who

do it most.

G E T T I N G F R O M H E R E T O T H E R E 315

Do you see the problem yet?

Science is about the testing and refinement of hypotheses and theories.

In principle, the most important quality of a scientist should be their ability

to accept, with an open mind, evidence that challenges theories that they

had believed for many years. But scientists are human, and moreover they

know that the scientists that produced the new evidence are also human. In

particular, they know that when a result is reported that contradicts estab

lished conventional thinking, the new evidence is often found later on to

have been the result of experimental error. Thus, it is generally pretty hard

to get senior scientists to change their mind about things, even if your evi

dence is really strong. The legendary physicist Max Planck famously re

marked in the 1920s that "Science advances funeral by funeral" and this is

only barely an exaggeration: It can take wed over a decade for really funda

mental changes of understanding of aspects of science to become generally

accepted. A famous example in biology is the mechanism of action of mito

chondria, cellular components that we've heard a lot about in this book. 1

And inevitably, this resistance to new ideas carries over heavily into how se

nior scientists evaluate grant applications.

So far, so unproblematic. After all, a modest degree of resistance to

new ideas that you may not yet fully grasp is a good thing in some ways—

we wouldn't want the scientific consensus to flit from one new idea to an

other too easily either, because (as I just mentioned) new ideas are often

wrong. But the inertia that exists in scientific thinking is generally greater

than this happy medium. And unfortunately, it's not just inertia of ideas, it's

inertia of reputations. Senior scientists who have been appointed by the

government to evaluate their colleagues' grant applications are, essentially

by definition, members of the establishment. If they receive two applica

tions of equal scientific merit, only one of which they have the resources to

fund, and one is from a scientist who has a history of radical views about

what science may shortly achieve, while the other is from a scientist who

has never said anything outrageous in his life, you can bet that it's the latter

who will get the money.

And that's not all. Reviewers of grant applications are, of course, given

guidelines telling them what aspects of the applications' scientific merit or

demerit they should consider particularly important. One aspect that is in

variably high on this list, if not at the very top, is feasibility: perceived likeli-

hood that the investigator will complete the proposed experimental program

within the time and budget requested and obtain results that will merit pub

lication in a reputable scientific journal. Sounds pretty uncontroversial,


doesn't it?—but in fact this policy is a huge problem for science, because it is

not (in practice) weighted by scientific significance. That's to say: A proposal

for a study that will almost certainly tell us something whatever its outcome

will fare much better in peer review than a study that may wed ted us noth

ing, even if what the second study might ted us is far more important than

what any outcome of the first study would ted us. This bias in favor of low-

risk, low-gain research at the expense of high-risk, high-gain research per

vades the whole of science and is extremely strong in biogerontology.

Well, I've spent quite a while in this chapter denouncing the stubborn

closed-mindedness of senior scientists, but I hope you've taken on board

that in the past couple of paragraphs I've explained that it's not entirely their

fault: it's really the fault of their paymasters, the public funding agencies,

a.k.a. the government. Grant reviewers are also grant recipients, by and

large (though they don't review their own applications, of course). Thus, if

the funding agency makes it known—either explicitly via written guidelines,

or implicitly by their actions and off-the-record remarks—that they would

prefer to fund middle-of-the road people to do dependable work than to

fund troublemakers to do controversial work, the reviewers are hardly likely

to dissent. It would be a very good thing if more such scientists did resist

this sort of instruction, but realistically that's too much to ask.

But actually . . . it's not the government's fault either. The real culprit is

you, the public.

This should not be a surprise to you. It's hardly a secret that govern

ments in all democracies ultimately act to achieve one thing above all oth

ers: their own re-election. That will not be aided if the government spends,

and is seen to spend, appreciable amounts of taxpayers' money on what the

public regards as blue-sky pipe dreams: research that will probably lead

nowhere. If the public were scientifically mature enough to appreciate that,

in the long run, the rate of scientific progress is slowed by this overcautious

approach, their elected representatives would be able to exercise similar vi

sion and to instruct grant reviewers accordingly. But the public do not ade

quately understand how science works, so this doesn't happen. (A similar

and even worse problem exists when it comes to medicine; I'll explore that

topic later in this chapter.) This is basically because the judgment of how

likely a hypothesis is to be true, or of how likely an experimental result is to

lead to further knowledge, is actually one of the most sophisticated and un-

teachable aspects of doing science.

In biogerontology, however, there is potentially a way out—and this

brings me back full circle (or triangle!) to the thing that distinguishes


biogerontology from all other scientific fields in terms of its interaction

with the public: the sheer extent of that interaction. Though there is no

hope of turning the public into scientists sophisticated enough to under

stand the merits of highly ambitious experiments, there is ample chance

simply to ted them that such-and-such an experimental approach is well

worth pursuing. There's probably not enough chance of this for most sci

entific fields, but in the case of biogerontology it's abundantly possible. So,

why don't biogerontologists do just that whenever they find themselves in

front of a camera? I already told you: They don't want to gain a reputation

for irresponsibility among their peers, because to do so would be to jeopar

dise their own chances of being funded even for unambitious work.

So there you have it—the triangular logjam. Biogerontologists are cau

tious in what they say to the public, in order to protect their funding, which

is provided by the government, which are cautious in what and whom they

fund, in order to protect their votes, which are provided by the public, who

are fatalistic about what's even worth trying to achieve, because they see the

biogerontologists saying only cautious things on the TV.

In order to defeat aging any time soon, I believe that an essential first

step must be to break the triangular logjam. How can this be done?

Since I entered biogerontology, I've been chipping away primarily at

one corner of the triangle: my fellow biogerontologists, especially the se

nior ones. Scientists are very politically aware, as described above, but

they're also honest and sincere people. Moreover—and this is a key point—

hardly any biogerontologists suffer from the pro-aging trance themselves.

They know full well how horrific aging is, and with very few exceptions

they want an end to it just as much as I do. Thirdly, there aren't very many

of them, so personal contact is easy: I've known essentially everyone in the

field personally for several years now. And finally, they're all smart enough

to have earned doctorates. All in all, if I have a good strong case that we

may be much closer to fixing aging than people have hitherto realized,

shouldn't I be able to convince them—and even convince them to say so

publicly?

Wed, not quite—but nearly. As in any walk of life, what people say is

important but what they don't say is also important. Those of my col

leagues to whom I have presented the SENS panel in detail have mostly

concluded that it is not fantasy, even though it's certainly very ambitious—

but that hasn't translated into explicit public calls for SENS to be funded.

What it has led to, however, is a variety of demonstrations of tacit support.

It started with coauthorship by five senior colleagues of the first paper on


SENS, which arose from a workshop in 2000 (see Chapter 4); it's continued

with refusal of several eminent colleagues to coauthor a denunciation of

SENS published in the respected journal EMBO Reports and orchestrated

by some of the less open-minded members of the community;2 and most re

cently it's included the remarkable development that some people who did

sign that denunciation have taken the initiative to divorce themselves from

it by publishing constructive responses to the SENS agenda, 3 , 4 something

that the EMBO Reports tirade specifically counselled against. While this

may seem pretty tame as seen from the outside, I can assure you that it's an

about-face as thorough as one ever sees in science.

It's obviously not enough, though. But it's all I'm likely to get from my

senior colleagues in biogerontology for the time being, i.e., until I can piece

together enough funding to give SENS research serious momentum despite

its radical nature. Thus, in the (hopefully brief!) meantime I must address

the other points of the triangle, too.

It's just conceivable that the government could be influenced directly.

There are visionaries in government, and just occasionally they find a way

to realize those visions. But in order to have any real chance on Capitol Hill

or its counterparts in other countries, you really have to know the minds of

the major players well—and that is something you don't pick up overnight.

Thus, I've continued to leave that strategy to others—and I'm delighted to

say that the ball seems to be slowly being picked up, most notably with the

splendid "Longevity Dividend" initiative, a new effort spearheaded by the

veteran lobbyist Dan Perry of the Alliance for Aging Research in collabora-

tion with three gerontologists.5 Whether they have much chance of success

remains to be seen, but I emphatically wish them luck.

As I've become more prominent, however, I have been able to start ad

dressing the third corner of the logjam: the public. You may recall that I

started this book with a somewhat cantankerous complaint to the effect

that if it weren't for the pro-aging trance I would be able to get on with the

actual science and technology of defeating aging. Well, that's certainly

true—but once given the chance, I have thrown as much energy into my

advocacy and outreach efforts as I was already throwing into the science.

Apart from anything else, I'm aware that the public are a source of funds in

their own right, as well as a source of pressure on governments to alter their

funding priorities.

The pro-aging trance dominates the nature of my interaction with the

media, and via them with the public. The overwhelming majority of my

time in interviews is occupied in discussions of the desirability of defeating


aging, rather than the feasibility. But the good news, which I encounter

mercifully often, is that it generally takes only a little bit of probing to re

veal that the ultimate basis of my interlocutor's concern is their reluctance

to accept the feasibility. It is this that convinces me so thoroughly that the

achievement of robust mouse rejuvenation will consign the pro-aging

trance to history in the twinkling of an eye.

The Intensity of the War on Aging, and Its Consequent

Likely Duration

In order to give you a sense of what the world is likely to be like after RMR

is achieved, I'm going to review some basic epidemiological and biomedical

facts about three well-known viruses—HIV, CMV, and avian flu—and then

examine an interesting scenario.

HIV has become one of the world's major killers. Belatedly, drugs that

can suppress it and prevent it from progressing to full-blown AIDS are

gradually becoming available in the developing world—still nowhere near

in the quantities needed, but maybe soon even in those quantities. In the

developed world, however, HIV is in a meaningful sense under control. It's

possible to live with HIV for decades without any symptoms whatsoever,

by the regular administration of expensive but (in the West) affordable

drugs. What we still don't have, of course, are two key things:

• a drug to eliminate HIV from the body;

• a vaccine to stop it from infecting people.

CMV, cytomegalovirus, is not one of the world's major killers. Wed, not

obviously. In people with a normal immune system, it is completely sup

pressed and causes no symptoms at all. (My "not obviously" qualification

arises from the fact that this suppression gradually wears down the immune

system during aging, so that eventually people become more susceptible to

more aggressive infections such as pneumonia; in this sense CMV is indi

rectly life-threatening. For more details on this and what we need to do

about it, see Chapter 10.) But it is incredibly widespread: most Westerners

are infected with it.

Avian flu is big news as I write these words (mid-2007), because for the

past few years we have been somberly informed that it could soon mutate

into a form that would cause a pandemic and potentially kid tens of millions


or even hundreds of millions of people. Ad that needs to happen is for the

avian flu virus to acquire genetic changes so that it can easily be passed from

humans to other humans, the same as more familiar (and much less deadly)

flu viruses can do. Such mutations are rare, but not astronomically rare; this

could happen any time. Vaccines for avian flu are under development, but

how well they will work depends on what mutations the virus picks up in the

process of becoming human-to-human transmissible, and anyway vaccines

often don't work so well on the elderly, who will be most at risk. Hence the

possible death rates.

I've summarized these viruses as background for a scenario that I now

want to explore in some detail, by way of an analogy with the situation after

RMR has been achieved. I needed to lay out this background so that you

appreciate that the scenario is reasonably realistic; I don't think I'll have

any trouble convincing you that it's a valid analogy.

Let's suppose that HIV mutated to become transmissible by air, just

like flu.

That's it. That's the situation I want to explore. Nothing else changes:

the drugs to suppress HIV still work, they're still pretty expensive, and vac

cines for HIV are still far away from development.

In this scenario, it's essentially certain that almost everyone in the

world would have HIV within a couple of years. Not everyone gets flu in a

pandemic, of course, but the difference is that once you get flu, if you don't

die you mount an immune response that actually works, i.e., that eliminates

the virus from your body. Thus, any given individual is infectious only for a

rather short period (and after they've recovered, they can't be infected

again, either). In the scenario we're looking at, once you get it you have it

forever, and you're infectious forever. There will be no hiding place.

Pretty apocalyptic, isn't it? (Lucidly, virologists think that in actual fact

this scenario is vastly more unlikely than the corresponding mutation for

avian flu.)

Well, hang on—is it so apocalyptic? We do have these drugs . . .

Let's look at a few round numbers. In the United States, roughly one

person in every 250 has HIV, according to the Populations Reference

Bureau—that's about one million people. The drug treatment to keep HIV

under control costs about $30,000 per year, so that adds up to about $30

billion per year. Thus, if everyone in the United States had HIV, we'd be

talking about $30 trillion per year. But the actual cost of production of

these drugs is far, far lower: generic forms of them are being synthesized in


India and sold (still at a profit, mind) for only $300 per year, and even lower

prices are in the offing. So actually we're looking at only $300 billion per

year—$1 billion per day—to keep everyone in the United States healthy

even if they all have HIV.

Now, a couple of points. First, you might think that "only $300 bil

lion per year" is a pretty curious use of the word "only." Well, think

again, because that's almost exactly what the United States is currently

spending on the war in Iraq. (I'm not commenting here on the relative

merits of these expenditures, you understand—I'm just pointing out that

we have a precedent of an unexpected expense of the same size that is not

bankrupting the nation.) Second, you might be against the infringing of

patents, so you might object to my slashing the cost by a factor of a hun

dred. But is your belief in the patent system stronger than your belief in

stopping your neighbors—or yourself, or your family—from coming

down with AIDS and dying horribly? Ask yourself honestly: If this sce

nario actually happened, and one major party campaigned on a manifesto

to raise taxes by $300 per year for the average person and to spend that

money on generic drugs to prevent AIDS, and the other party cam

paigned on a commitment either to raise taxes by $30,000 per year for the

average person or not to provide the drugs at all, who do you seriously

think would get elected?

I hope I've convinced you what would happen in the above scenario:

we would find the resources to treat everyone. We'd probably find the re

sources to treat everyone in the developing world, too, just as we're now

stirring ourselves to treat everyone who needs such drugs in the developing

world today.

Now, let's look at society's post-RMR view of aging in the same way. I

suspect you can quickly see the similarities. Everyone has aging. The ther

apies we'll be looking to make available will be suppression therapies,

which we will have to take for as long as we live (though much less fre

quently than those with HIV need to take their drugs). Within that limita

tion, however, the therapies will work: people's aging won't progress. But

the therapy will be very expensive. (In the first instance that expense will

be mainly for funding of research, training greatly increased numbers of

medical personnel, building additional drug synthesis facilities and such

like. The same figure I discussed above, $1 billion per day, is as good an es

timate as any.)

So let's ask the opposite question: what are the differences between a


post-RMR world and a universal-HIV world? I would say that there are re

ally only two:

• the therapies won't yet exist at the time RMR is achieved;

• our acceptance that human aging can probably be defeated fairly

soon will be new, while the universality of aging is age-old: this is

the reverse of the situation with HIV in the above scenario.

I would argue that neither of these differences has any real chance of

causing society to behave any differently in the aftermath of RMR than in

the universal-HIV scenario. The nonexistence of the therapies is really no

different than the nonexistence of enough antiretroviral drugs, which

would certainly be the initial situation in the scenario I've described: we

will work to develop those therapies as fast as possible, just as we would

work to scale up production of antiretrovirals as fast as possible. The idea

that the order of events could matter seems equally far-fetched; if everyone

has a life-threatening health condition and we have a shot at making it no

longer life-threatening, we'd clearly strive to do so.

Why "the War on Aging"?

I think you can probably see by now my reasons for calling this period "the

War on Aging." In the early 1970s, there was an initiative called "the War

on Cancer" that involved a sharp and sustained hike in the funding for can

cer research fueled by the hope that cancer could be cured within as few as

five years. 6 The war on cancer was not as abject a failure as some people

tend to suggest—without that funding we would not have advanced nearly

as fast as we have in our understanding of cancer, so there's little doubt that

that initiative will have brought forward the true defeat of cancer quite

substantially—but it was a complete misnomer, for one simple reason: the

amount of money involved was really quite small, imperceptible to the U.S.

taxpayer. As summarized above, the war on aging will be extremely

expensive—not imperceptible at all. And yet, it is clear that the public will

embrace the necessary tax rises: it will be quite obviously impossible to get

elected except on a manifesto commitment to attack aging with all avail

able resources. This is a mind-set that has previously been seen only at one

type of stage in a wealthy nation's history: wartime.


Hippocrates and Gelsinger

In closing this chapter, I want to touch on one final aspect of the war on

aging—one which completes my case that it may well last only 15-20 years.

In 1999, a teenager named Jesse Gelsinger died of anaphylactic shock in

a trial of a gene therapy procedure at a hospital in Philadelphia. 7 This was the

first such incident of its kind, and it sent the gene therapy world into its own

form of anaphylactic shock. The bottom l i n e was that essentially all gene

therapy trials worldwide were suspended for about a year. We don't know

how much delay that will eventually turn out to translate into in terms of the

development of safe and effective gene therapy, but the chances are pretty

good that it'll be a few weeks at least, and given the enormous breadth of ap

plicability of gene therapy, that could mean thousands of lives lost—maybe

even hundreds of thousands if it delays the defeat of aging. Bearing this in

mind, was the suspension of trials for so long a proportionate response?

The U.S. Food and Drug Administration (FDA) would answer in the af

firmative, as would their counterparts around the world. Regulation of exper

imental drugs and therapies, whether it be in terms of what results are

needed or how they are obtained, is based on one abiding principle above all

others: the minimization of risk that the therapy might make the patient

worse. Specifically, this minimization of risk explicitly counts for more, much

more, than maximizing benefit. In this way, the FDA is following a principle

that has existed since medicine's earliest days: the famous edict of Hip

pocrates, primum non nocere, or "first do no harm." (Note that this phrase is

actually not part of the Hippocratic Oath, the set of principles by which med

ical professionals swear to abide as part of their qualification process.)

I take the view, quite simply, that Hippocrates has had his day. The

avoidance of harm was a rational strategy to adopt during the early days of

medicine, when people very often recovered spontaneously from what their

doctors thought were fatal conditions simply because the doctors had inad

equate diagnostic tools. In such a situation, the psychological effect of pos

sibly causing harm, whether it be the effect on the doctor or on the patient's

loved ones, legitimately skews the objective cost-benefit analysis of a given

treatment. In the modern world, however, such recoveries are relatively

very rare. I therefore believe that the 10:1 (at least) ratio of lives lost

through slow approval of safe drugs to lives lost through hasty approval of

unsafe drugs 8 is no longer acceptable.

Furthermore, I believe that in the turbulence of the War on Aging, the

general public will also come to the view that it is unacceptable. This will


lead, in a matter of months from the achievement of RMR, to a root-and-

branch revision of the laws and regulations governing clinical trials and ap

proval of drugs and therapies. A fair guess is that drugs will be approved

for universal use (via prescription) after a degree of testing that approxi

mates today's Phase 2. People will die as a result; the 10:1 ratio mentioned

above will probably reduce to 2:1. And people will be happy about this

change, because they'll know that it's wartime, and the first priority—even

justifying considerable loss of life in the short term—is to end the slaughter

as soon as humanly possible. I am the first to acknowledge that, without

such a change of priorities, my prediction that the war on aging may well

last only fifteen years would be totally absurd. But with that change, only

the pace of research will be limiting.

14

B o o t s t r a p p i n g O u r W a y t o

a n A g e l e s s F u t u r e

I have a confession to make. In Chapters 5 through 12, where I

explained the details of SENS, I elided one rather important fact—a fact

that the biologists among my audience will very probably have spotted. I'm

going to address that omission in this chapter, budding on a line of reason

ing that I introduced in an ostensibly quite circumscribed context toward

the end of Chapter 9.

It is this: The therapies that we develop in a decade or so in mice, and

those that may come only a decade or two later for humans, will not be per

fect. Other things being equal, there will be a residual accumulation of

damage within our bodies, however frequently and thoroughly we apply

these therapies, and we will eventually experience age-related decline and

death just as now, only at a greater age. Probably not all that much greater

either—probably only thirty to fifty years older than today.

But other things won't be equal. In this chapter, I'm going to explain

why not—and why, as you may already know from other sources, I expect

many people alive today to live to one thousand years of age and to avoid

age-related health problems even at that age.

I'll start by describing why it's unrealistic to expect these therapies to

be perfect.


Evolution Didn' t Leave Notes

I emphasized in Chapter 3 that the body is a machine, and that that's both

why it ages and why in principle it can be maintained. I made a comparison

with vintage cars, which are kept fully functional even one hundred years

after they were built, using the same maintenance technologies that kept

them going fifty years ago when they were already far older than they were

ever designed to be. More complex machines can also be kept going indef

initely, though the expense and expertise involved may mean that this never

happens in practice because replacing the machine is a reasonable alterna

tive. This sounds very much like a reason to suppose that the therapies we

develop to stave off aging for a few decades will indeed be enough to stave

it off indefinitely.

But actually that's overoptimistic. All we can reliably infer from a com

parison with man-made machines is that a truly comprehensive panel of

therapies, which truly repairs everything that goes wrong with us as a result

of aging, is possible in principle—not that it is foreseeable. And in fact, if

we look back at the therapies I've described in this book, we can see that

actually one thing about them is very unlike maintenance of a man-made

machine: these therapies strive to minimally alter metabolism itself, and tar

get only the initially inert side effects of metabolism, whereas machine

maintenance may involve adding extra things to the machinery itself (to

the fuel or to the oil of a car, for example). We can get away with this sort

of invasive maintenance of man-made machines because we (well, some of

us!) know how they work right down to the last detail, so we can be ade

quately sure that our intervention won't have unforeseen side effects.

With the body—even the body of a mouse—we are still profoundly igno

rant of the details, so we have to sidestep our ignorance by interfering as

little as possible.

What that means for efficacy of therapies is that, as we fix more and

more aspects of aging, you can bet that new aspects will be unmasked.

These new things—eighth and subsequent items to add to the "seven

deadly things" listed in this book—will not be fatal at a currently normal

age, because if they were, we'd know about them already. But they'll be fa

tal eventually, unless we work out how to fix them, too.

It's not just "eighth things" we have to worry about, either. Within each

of the seven existing categories, there are some subcategories that will be

easier to fix than others. For example, there are lots of chemically distinct

cross-links responsible for stiffening our arteries; some of them may be

B O O T S T R A P P I N G O U R W A Y 327

broken with alagebrium and related molecules, but others will surely need

more sophisticated agents that have not yet been developed. Another ex

ample: obviating mitochondrial DNA by putting modified copies of it into

the cell's chromosomes requires gene therapy, and thus far we have no gene

therapy delivery system ("vector") that can safely get into all cells, so for the

foreseeable future we'd probably only be able to protect a subset of cells

from mtDNA mutations. Much better vectors will be needed if we are to

reach all cells.

In practice, therefore, therapies that rejuvenate sixty-year-olds by

twenty years will not work so well the second time around. When the ther

apies are applied for the first time, the people receiving them will have sixty

years of "easy" damage (the types that the therapies can remove) and also

sixty years of "difficult" damage. But by the time beneficiaries of these

therapies have returned to biologically sixty (which, let's presume, will hap

pen when they're chronologically about eighty), the damage their bodies

contain will consist of twenty years of "easy" damage and eighty years of

"difficult" damage. Thus, the therapies will only rejuvenate them by a

much smaller amount, say ten years. So they'd have to come back sooner

for the third treatment, but that will benefit them even less . . . and very

soon, just like Achilles catching up with the tortoise in Zeno's paradox, ag

ing will get the better of them. See Figure 1.

Back in Chapters 3 and 4, I explained that, contrary to one's intuition,

rejuvenation may actually be easier than retardation. Now it's time to intro

duce an even more counterintuitive fact: that, even though it will be much

harder to double a middle-aged human's remaining life span than a middle-

aged mouse's, multiplying that remaining life span by much larger factors—

ten or thirty, say—will be much easier in humans than in mice.

The Two-Speed Pace of Technology

I'm now going to switch briefly from science to the history of science, or

more precisely the history of technology.

It was well before recorded history that people began to take an inter

est in the possibility of flying: indeed, this may be a desire almost as ancient

as the desire to live forever. Yet, with the notable but sadly unreproduced

exception of Daedalus and Icarus, no success in this area was achieved

until about a century ago. (If we count balloons then we must double that,

but really only airships—balloons that can control their direction of travel


Figure 1. The diminishing returns delivered by repeated application of a rejuvenation regime.

reasonably well—should be counted, and they only emerged at around the

same time as the airplane.) Throughout the previous few centuries, engi

neers from Leonardo on devised ways to achieve controlled powered flight,

and we must presume that they believed their designs to be only a few de

cades (at most) from realization. But they were wrong.

Ever since the Wright brothers dew at Kitty Hawk, however, things

have been curiously different. Having mastered the basics, aviation engi

neers seem to have progressed to ever greater heights (literally as well as

metaphorically!) at an almost serenely smooth pace. To pick a representa

tive selection of milestones: Lindbergh dew the Atlantic twenty-four years

after the first powered flight occurred, the first commercial jetliner (the

Comet) debuted twenty-two years after that, and the first supersonic air

liner (Concorde) followed after a further twenty years.

This stark contrast between fundamental breakthroughs and incre

mental refinements of those breakthroughs is, I would contend, typical of

the history of technological fields. Further, I would argue that it's not sur

prising: both psychologically and scientifically, the difficulty of bigger ad

vances is harder to estimate.

I mention all this, of course, because of what it tells us about the likely

future progress of life extension therapies. Just as people were wrong for

centuries about how hard it was to fly but eventually cracked it, we've been

wrong since time immemorial about how hard aging is to combat but we'll


eventually crack it, too. But just as people have been pretty reliably correct

about how to make better and better aircraft once they had the first one, we

can expect to be pretty reliably correct about how to repair the damage of

aging more and more comprehensively once we can do it a little.

That's not to say it'll be easy, though. It'll take time, just as it took time

to get from the Wright Flyer to Concorde. And that is why, if you want to

live to one thousand, you can count yourself lucky that you're a human and

not a mouse. Let me take you through the scenario, step by step.

Suppose we develop Robust Mouse Rejuvenation in 2016, and we take a

few dozen two-year-old mice and duly treble their one-year remaining life

spans. That will mean that, rather than dying in 2017 as they otherwise

would, they'd die in 2019. Well, maybe not—in particular, not if we can de

velop better therapies by 2018 that re-treble their remaining life span (which

will by now be down to one year again). But remember, they'd be harder to

repair the second time: their overall damage level may be the same as before

they received the first therapies, but a higher proportion of that damage will

be of types that those first therapies can't fix. So we'd only be able to achieve

that re-trebling if the therapies we have available by 2018 are considerably

more powerful than those that we had in 2016. And to be honest, the chance

that we'd improve the relevant therapies that much in only two years is ready

pretty slim. In fact, the likely amount of progress in just two years is so small

that it might as well be considered zero. Thus, our murine heroes will indeed

die in 2019 (or 2020 at best), despite our best efforts.

But now, suppose we develop Robust Human Rejuvenation in 2031,

and we take a few dozen sixty-year-old humans and duly double their

thirty-year remaining life spans. By the time they come back in, say, 2051,

biologically sixty again but chronologically eighty, they'd need better thera

pies, just as the mice did in 2018. But luckily for them, we'll have had not

two but twenty years to improve the therapies. And twenty years is a very

respectable period of time in technology—long enough, in fact, that we will

with very high probability have succeeded in developing sufficient im

provements to the 2031 therapies so that those eighty-year-olds can indeed

be restored from biologically sixty to biologically forty, or even a little

younger, despite their enrichment (relative to 2031) in harder-to-repair

types of damage. So unlike the mice, these humans will have just as many

years (twenty or more) of youth before they need third-generation treat

ments as they did before the second.

And so on . . . see Figure 2.


Figure 2. How the diminishing returns depicted in Figure 1 are avoided by repeated application of a rejuvenation regime that is sufficiently more effective each time than the previous time.

Longevity Escape Velocity

The key conclusion of the logic I've set out above is that there is a threshold

rate of biomedical progress that will allow us to stave off aging indefinitely,

and that that rate is implausible for mice but entirely plausible for humans.

If we can make rejuvenation therapies work well enough to give us time to

make them work better, that will give us enough additional time to make

them work better still, which wi l l . . . you get the idea. This will allow us to

escape age-related decline indefinitely, however old we become in purely

chronological terms. I think the term "longevity escape velocity" (LEV)

sums that up pretty well.1

One feature of LEV that's worth pointing out is that we can accumu

late lead time. What I mean is that if we have a period in which we improve

the therapies faster than we need to, that will allow us to have a subsequent

period in which we don't improve them so fast. It's only the average rate of

improvement, starting from the arrival of the first therapies that give us just

twenty or thirty extra years, that needs to stay above the LEV threshold.

In case you're having trouble assimilating all this, let me describe it in

terms of the physical state of the body. Throughout this book, I've been dis

cussing aging as the accumulation of molecular and cellular "damage" of


various types, and I've highlighted the fact that a modest quantity of dam

age is no problem—metabolism just works around it, in the same way that

a household only needs to put out the garbage once a week, not every hour.

In those terms, the attainment and maintenance of longevity escape veloc

ity simply means that our best therapies must improve fast enough to out

pace the progressive shift in the composition of our aging damage to more

repair-resistant forms, as the forms that are easier to repair are progres

sively eliminated by our therapies. If we can do this, the total amount of

damage in each category can be kept permanently below the level that ini

tiates functional decline.

Another, perhaps simpler, way of looking at this is to consider the anal

ogy with literal escape velocity, i.e. the overcoming of gravity. Suppose

you're at the top of a cliff and you jump off. Your remaining life expectancy

is short—and it gets shorter as you descend to the rocks below. This is ex

actly the same as with aging: The older you get, the less remaining time you

can expect to live. The situation with the periodic arrival of ever better re

juvenation therapies is then a bit like jumping off a cliff with a jet pack on

your back. Initially the jet pack is turned off, but as you fall, you turn it on

and it gives you a boost, slowing your fall. As you fad farther, you turn up

the power on the jet pack, and eventually you start to pull out of the dive

and even start shooting upward. And the farther up you go, the easier it is

to go even further.

The Political and Social Significance of Discussing LEV

I've had a fairly difficult time convincing my colleagues in biogerontology

of the feasibility of the various SENS components, but in general I've been

successful once I've been given enough time to go through the details.

When it comes to LEV, on the other hand, the reception to my proposals

can best be described as blank incomprehension. This is not too surprising,

in hindsight, because the LEV concept is even further distant from the sort

of scientific thinking that my colleagues normally do than my other ideas

are: it's not only an area of science that's distant from mainstream gerontol

ogy, it's not even science at all in the strict sense, but rather the history of

technology. But I regard that as no excuse. The fact is, the history of tech

nology is evidence, just like any other evidence, and scientists have no right

to ignore it.

Another big reason for my colleagues' resistance to the LEV concept is,


of course, that if I'm seen to be right that achievement of LEV is foresee

able, they can no longer go around saying that they're working on postpon

ing aging by a decade or two but no more. As I outlined in Chapter 13,

there is an intense fear within the senior gerontology community of being

seen as having anything to do with radical life extension, with all the un

certainties that it will surely herald. They want no part of such talk.

You might think that my reaction to this would be to focus on the short

term: to avoid antagonising my colleagues with the LEV concept and its

implications of four-digit life spans, in favor of increased emphasis on the

fine details of getting the SENS strands to work in a first-generation form.

But this is not an option for me, for one very simple and incontrovertible

reason: I'm in this business to save lives. In order to maximize the number

of lives saved—healthy years added to people's lives, if you'd prefer a more

precise measure—I need to address the whole picture. And that means en

suring that you, dear reader—the general public—appreciate the impor

tance of this work enough to motivate its funding.

Now, your first thought may be: Hang on, if indefinite life extension is

so unpalatable, wouldn't funding be attracted more easily by keeping quiet

about it? Well, no—and for a pretty good reason.

The world's richest man, Bid Gates, set up a foundation a few years ago

whose primary mission is to address health issues in the developing world. 2

This is a massively valuable humanitarian effort, which I wholeheartedly

support, even though it doesn't directly help SENS at all. I'm not the only

person who supports it, either: In 2006 the world's second richest man,

Warren Buffett, committed a large proportion of his fortune to be donated

in annual increments to the Gates Foundation.3

The eagerness of extremely wealthy individuals to contribute to world

health is, in more general terms, an enormous boost for SENS. This is

mainly because a rising tide raises all boats: once it has become acceptable

(even meritorious) among that community to be seen as a large-scale health

philanthropist, those with "only" a billion or two to their name will be

keener to join the trend than if it is seen as a crazy way to spend your hard-

earned money.

But there's a catch. That logic only works if the moral status of SENS is

seen to compare with that of the efforts that are now being funded so well.

And that's where LEV makes all the difference.

SENS therapies will be expensive to develop and expensive to admin

ister, at least at first. Let's consider how the prospect of spending all that

money might be received if the ultimate benefit would be only to add a cou-


ple of decades to the lives of people who are already living longer than most

in the developing world, after which those people would suffer the same

duration of functional decline that they do now.

It's not exactly the world's most morally imperative action, is it?

Indeed, I would go so far as to say that, if I were in control of a few bil

lion dollars, I would be quite hesitant to spend it on such a marginal im

provement in the overall quality and quantity of life of those who are

already doing better in that respect than most, when the alternative exists

of making a similar or greater improvement to the quality and quantity of

life of the world's less fortunate inhabitants.

The LEV concept doesn't make much difference in the short term to

who would benefit from these therapies, of course: it will necessarily be

those who currently die of aging, so in the first instance it will predomi

nantly be those in wealthy nations. But there is a very widespread appreci

ation in the industrialised world—an appreciation that, I feel, extends to

the wealthy sectors of society—that progress in the long term relies on aim

ing high, and in particular that the moral imperative to help those at the

rear of the field to catch up is balanced by the moral imperative to maxi

mize the average rate of progress across the whole population, which ini

tially means helping those who are already ahead. The fact that SENS is

likely to lead to LEV means that developing SENS gives a huge boost to the

quality and quantity of life of whomever receives it: so huge, in fact, that

there is no problem justifying it in comparison to the alternative uses to

which a similar sum of money might be put. The fact that life span is ex

tended indefinitely rather than by only a couple of decades is only part of

the difference that LEV makes, of course: arguably an even more important

difference in terms of the benefit that SENS gives is that the whole of that

life will be youthful, right up until a beneficiary mistimes the speed of an

oncoming truck. The average quality of life, therefore, will rise much more

than if all that was in prospect were a shift from, say, 7:1 to 9:1 in the ratio

of healthy life to frail life.

Quantifying Longevity Escape Velocity More Precisely

This chapter has, I hope, closed down the remaining escape routes that

might still have remained for those still seeking ways to defend a rejection of

the SENS agenda. I have shown that SENS can be functionally equivalent to

a way to eliminate aging completely, even though in actual therapeutic terms


it will only be able to postpone aging by a finite amount at any given mo

ment in time. I've also shown that this makes it morally just as desirable—

imperative, even—as the many efforts into which a large amount of private

philanthropic funding is already being injected.

I'm not complacent though: I know that people are quite ingenious

when it comes to finding ways to avoid combating aging. Thus, in order to

keep a few steps ahead, I have recently embarked on a collaboration with a

stupendous programmer and futurist named Chris Phoenix, in which we are

determining the precise degree of healthy life extension that one can expect

from a given rate of progress in improving the SENS therapies. This is lead

ing to a series of publications highlighting a variety of scenarios, but the short

answer is that no wool has been pulled over your eyes above: the rate of

progress we need to achieve starts out at roughly a doubling of the efficacy of

the SENS therapies every forty years and actually declines thereafter. By

"doubling of efficacy" I mean a halving of the amount of damage that still

cannot be repaired.

So there you have it. We will almost certainly take centuries to reach

the level of control over aging that we have over the aging of vintage cars—

totally comprehensive, indefinite maintenance of full function—but be

cause longevity escape velocity is not very fast, we will probably achieve

something functionally equivalent within only a few decades from now, at

the point where we have therapies giving middle-aged people thirty extra

years of youthful life.

I think we can cad that the fountain of youth, don't you?

15

War B o n d s fo r t h e

C a m p a i g n A g a i n s t A g i n g

It is, as you now know, my bold but solidly grounded contention

that there is a strong chance that you—the reader of this book—will live to

experience the rejuvenation of your body into a flesh that is years or even

decades younger, biologically, than your chronological age, leading ulti

mately to an endless summer of literally perpetual youth. But that is a pre

diction about what could be—not about what must be. Make no mistake:

Once the War on Aging begins, it must end in victory, and the future of in

definite health will be ours. But whether that process begins in time to save

our parents, or only ourselves, or only our children, or even their children

depends entirely on when the first bomb of that war—the achievement of

robust mouse rejuvenation (RMR)—is finally dropped. So with that under

standing, the key question for each of us is, What am I going to do about it?

Granted that the War on Aging could begin in as little as a decade, it

makes sense to take care of yourself and your family, so that you don't miss

out on the arrival of robust human rejuvenation by just a few years. There is

plenty of well-established science on this front: eat more fruits and vegetables,

get your essential fatty acids, exercise, and maintain a healthy weight. But a

much more effective way to increase your personal odds of seeing your body

rejuvenated—and one that has the decided advantage that it also increases


the odds of survival for those close to you, and for untold thousands that you

have never even met—is to hasten the day when the battle is well and truly

joined. Fortunately, there are some very powerful things that you can do, to

day, to help ensure the saving of lives, again of tens of thousands of lives a day,

possibly including your own or your most dearly beloved. The most immedi

ately obvious actions would be to lobby for more funding for rejuvenation re

search, and for the crucial lifting of restrictions on federal funding to

embryonic stem cell research in the United States, by writing letters to your

political representatives, demanding change.

But an even more powerful thing you can do is to donate to the

Methuselah Foundation.

Let's step back a moment to remind ourselves of where we are today,

and see how we can affect our future.

Remember the logjam that I outlined in Chapter 13? The reason why

the investments necessary to bring forward robust mouse rejuvenation—

the first and critical benchmark for the instigation of a total life-and-death

struggle against biological aging—are so hard to obtain lies in a mutually

reinforcing ring of politically directed funding restrictions, scientific over-

caution in public statements and grant requests, and public opinion. The

fastest way out of this vicious circle is to create an independent source of

funding, pouring the needed billion or so dollars directly into work de

signed to achieve RMR. Unfortunately, it would be very difficult to raise the

funds required to do this in a short time frame, precisely because of the

widespread pessimism engendered in the public by scientists afraid for

their careers in a world where the logjam exists.

There are two plausible ways to change that, and the Methuselah Foun

dation is the worldwide spearhead for both of them.

The first is to support SENS research directly. You can do that by do

nating to the Methuselah Foundation, because we are a standard science

funding organization. Just like the National Institutes of Health or the Na

tional Science Foundation, our scientific team, headed by me as Chief Sci

ence Officer, evaluate scientific publications and research findings and

provide funds to professors around the world. The difference between us

and other agencies, of course, is that we are focused on a particular goal

and we are not afraid to fund projects that may take a long time to succeed.

Or . . . that may not succeed at all. And that's why, by way of hedging

our bets, we have the second strategy.

I believe that SENS is far and away the most promising way to achieve

RMR soon and corresponding human therapies thereafter—but, like any

W A R B O N D S F O R T H E C A M P A I G N 337

scientist, I could be wrong. Really hard technological goals, whether in

medicine or elsewhere, vary a lot in terms of how confident the experts in

the relevant field are that their preferred approach will work. At one ex

treme, in some cases there is almost no doubt about how to proceed—all

that holds the project back is availability of resources. The Apollo project

was a fine example of this: once national pride freed up the necessary cash,

the project went from start to finish faster than Boston's Big Dig. But at the

other extreme—powered flight before 1900, for example, or essentially all

medicine before 1800—people have ideas about what might work that are

still extremely speculative, and attempt after attempt fails or never even

gets tested. Testing everything that might work just costs too much for any

organization, even a highly motivated government, to afford when there are

so many comparably plausible possibilities.

Luckily, there is one time-tested strategy that has been successfully

used, again and again, to solve engineering challenges of this sort without

having to raise even a small fraction of the full sum required to complete

the project. That strategy is the research prize.

Research prizes with a specific benchmark have a long and illustrious

track record of producing the development of effective prototype tech

nologies with only a small investment of funds. Charles Lindbergh's famous

transatlantic flight in 1927; John Harrison's invention of a way to fix the

longitude location of a vessel at sea (crucial to successful navigation away

from a coastline); and the dramatic photo-finish race for the first privately

funded suborbital flight with human cargo that was driven by the Ansari

X-Prize, are all examples of the power of such prizes to spur daring tech

nological innovation.

What is so powerful about research prizes is that they only reward suc

cess. Not a single dollar of the prize goes out until someone achieves the

goal laid out by its creators. As a result, the existence of a single prize moti

vates many teams of independent scientists and engineers to go after it—

each of them using a different approach, and each of them investing their

own dollars independently. As a result, the money that is mistakenly in

vested in approaches that are ultimately shown to be unsuccessful does not

deplete the prize jackpot by a single penny. In the end, about ten to twenty

dollars is ultimately laid out by the contestants for every dollar raised to put

in the jackpot of a research prize—even though each contestant usually

gambles less private money than is sitting in the pot—and the goal of the

prize is achieved at a cost to the prize's principals that is far less than would

be required for a monolithic "Apollo Project" approach.


You can see where this is going.

The Methuselah Mouse Prize (or Mprize, with a tip of the hat to the re

cent success of the X Prize) is a project that was dreamed up independently

around the turn of the century by a few biogerontologists (starting with

Gregory Stock's concept of the Prometheus Prize) and by long-time hu

manitarian visionary David Gobel. When David and I discovered each

other, our complementary talents allowed us very rapidly to bring the prize

to fruition. The purpose of the project is to break the logjam that we've

been discussing using a research prize structured similarly to the X Prize

model. Enjoying the support of X Prize Chair and CEO Peter Diamandis as

a chief advisor, the Mprize's chief project is the Rejuvenation Prize for the

greatest extension of life span in mice that are already elderly—in other

words, for progress toward fully-fledged robust mouse rejuvenation.

The Mprize has the potential to remove the stumbling blocks that cur

rently restrict scientists in government and industry from taking on the ag

ing process as a curable disease. For the scientists in academia, it creates an

incentive to write the right grant proposals, in hopes of obtaining more

funding directly and greater prestige for their institutions by winning the

prize—prestige that itself tends to attract more funding from outside

sources.

But not only that: it's a popular win, too. The prize concept, by its na

ture, captures public imagination and provides a dramatic way to inform

the public and the media that scientists are working on extending healthy

life spans in mammals. This increases the credibility of any similar rep

utable efforts, and wins acceptance for the idea that it can be done in hu

mans. In turn, changes in public opinion ease political constraints on

awarding public funding for such projects, and may even generate active

pressure for such awards to be made before RMR has occurred.

And the Mprize also reorients the incentives for industry. Right now,

there is no specific motivation for private researchers to perform life span

studies in mice: at most, they are a stepping stone toward long, expensive,

human trials. When a significant financial reward—and the promise of sub

stantial publicity—is on the table, however, a business case is created for

spending a few years rather than a few months in testing a compound in

mice. Should a startup company succeed in rejuvenating mice, you can bet

that Big Pharma will be beating down its door for the rights to translate

their intervention to humans.

Thus, the Mprize can bypass the vicious circle that has put the chid on

serious biomedical gerontology in academic research. More than this: it can

W A R B O N D S F O R T H E C A M P A I G N 339

reverse its course, putting its converging, self-reinforcing mechanisms to

work in a new, virtuous circle. Scientific results will drive public optimism,

in turn driving political acceptability, leading to more public and private

funding. Those investments will eventually—maybe very rapidly—lead to

robust mouse rejuvenation even if the SENS approach were to falter; and

then, the War on Aging will begin in earnest.

Eat well, exercise, and support the Methuselah Foundation, and I shad

look forward to shaking your hand in a future where engineered negligible

senescence is a reality: where we can enjoy dramatically extended lives in a

new summer of vigor and health, the dark specter of the age plague driven

away by the sunshine of perpetual youth.

Glossary

2-deoxyglucose (2-DG): a compound that closely resembles blood sugar, but

unlike sugar cannot be metabolized into energy in the mitochondria. For a

while, it looked as if 2-DG were a calorie restriction mimetic.

Active vaccination: giving a person the antigen against which doctors want to

provide immune protection, to trigger the immune system to produce anti

bodies that will attack it.

Adaptive immune system: the branch of the immune system that learns about

and targets specific foreign and "hijacked" cells though their antigens. The

existence of the adaptive immune system provides the basis of vaccines.

Adenosine triphosphate: see ATP.

Adult stem cell: stem cells found in mature bodies, that can give rise to only a

relatively narrow range of specialized, mature cells. Compare embryonic

stem cell.

Advanced glycation endproducts (AGE): highly chemically stable compound

that results as the "end product" of a series of chemical reactions in glyca

tion chemistry.

Advanced lipoxidation endproducts (ALEs): stable chemical damage to pro

teins caused by their interactions with fats; similar to advanced glycation

endproducts.

Aging damage: from the practical viewpoint of the engineer's school of anti-aging

medicine, changes at the molecular level to the structure of the organism

364 G L O S S A R Y

that distinguish an organism that has been around for a long time from one

that has not. On an abstract, theoretical level, we would only want to in

clude those changes that actually contribute to biological aging—i.e., those

that contribute to the increasing risk of disease, dysfunction, and death as

we go on living. From the point of view of anti-aging medicine, however, this

distinction becomes problematic, because it would require us to first deter

mine which changes genuinely contribute to biological aging and which do

not—which would require many more decades of research. The engineer's

school of anti-aging medicine sidesteps this ignorance by classifying all ag

ing changes that might contribute to biological aging as "damage," and

then intervening to repair or obviate it.

Aging: the word is used in many senses, but the one that's important for our

purpose is biological aging.

Alagebrium: a drug that appears to break advanced glycation end-product cross

links. Chemically, 4,5-dimethyl-3-(2-oxo-2-phenylethyl)-thiazolium chlo

ride. Originally code-named ALT-711.

Allotopic expression (AE): Expression of proteins from a different (Greek allo-)

place (topos). The creation of "backup copies" in the nucleus of the

protein-coding genes now housed in mitochondrial DNA.

Alpha-diketone: an advanced glycation end-product cross-link. Hypothetically,

the AGE broken by alagebrium.

Alpha-secretase: an enzyme required for the normal processing of Amyloid

Precursor Protein. APP does not form beta-amyloid protein when it is pro

cessed by this enzyme.

ALT: see Alternative Lengthening of Telomeres pathway.

ALT-711: the original code-name of alagebrium.

Alternative Lengthening of Telomeres (ALT): a poorly understood mecha

nism whereby some cancer cells relengthen their telomeres without using

telomerase.

Amadori product: a somewhat stable intermediate compound of glycation

chemistry, linking Schiff bases to advanced glycation endproducts (AGE).

Glycated hemoglobin or HbA1c is an Amadori product.

Aminoguanidine: drug that inhibits the formation of advanced glycation end

products, first inhibiting the initial glycation reaction, and then reducing

glycoxidation through antioxidant and metal-chelating effects, and above

all through its ability to mop up oxoaldehydes. Trade name Pimagidine.

Amyloid beta: see beta-amyloid protein-:

Amyloid precursor protein (APP): a protein produced in the brain that, when

damaged, can form beta-amyloid protein. Has some essential function in

our bodies, possibly including being necessary to allow neurons to rewire

themselves in response to new learning and to grow out neurites.

Amyloid protein A amyloidosis (AA): an amyloidosis caused by the excessive

G L O S S A R Y 365

production of amyloid A protein, a protein involved in the inflammatory

response, usually resulting from chronic inflammatory conditions. The

most common amyloid disorder outside the United States. Also termed

"inflammatory" or "secondary" amyloidosis.

Amyloid: any one of a range of cell-snaring chains of molecules that are created

by damage to healthy proteins naturally present in the body, causing them to

become twisted out of their proper configuration in ways that cause them to

undergo toxic interactions with each other, or with other constituents of the

cell. Typically form chemically "sticky" "webs" around cell structures that in

hibit their functions. See for example beta-amyloid protein.

Amyloidoses: Diseases caused by the accumulation of amyloids.

Anergic T cells: T cells that can no longer carry out their duties.

Angiogenesis: the growth of new blood vessels.

Anti-aging medicine: Biomedical attempts to intervene in the pathological ef

fects of biological aging. See geriatrician's school, gerontologists' school, and

engineer's school of anti-aging medicine. Most of what is called "anti-aging

medicine" in the marketplace today is either sheer hokum, or is a mixture

of (a) crude and unproven attempts at the gerontologist's school of anti-

aging medicine (hormone shots, antioxidant vitamins), combined with ba

sic (though unfortunately rarely practiced) preventive medicine (improved

diet and exercise) and the geriatrician's school of anti-aging medicine.

Antibodies: Proteins that specifically recognize and bind to antigens of the or

ganisms they're intended to fight, either by flagging the invader for attack

by other components of the immune system, or by blocking receptors and

other proteins that are needed for the pathogen's survival.

Antigen: a protein recognized by the immune system.

Antigen-presenting cells (APCs): the immune system's reconnaissance teams,

which identify enemy combatants' antigens through direct encounters

with them or by digging through the rubble of old battlegrounds (the re

mains of cells ravaged by them)and then alert T cells specialized in waging

war against the specific invaders that carry them.

Antisense mRNA: genetic material that binds to a pre-defined transcribed

gene as it emerges, preventing it from being used to make the protein that

it encodes.

Apoptosis: often referred to as "programmed cell death" or "cellular suicide."

A carefully orchestrated programmed process of self-destruction carried

out in cells that have been hijacked by "enemy forces" (viruses or cancer,

for example) to prevent them from threatening the organism as a whole.

Also used extensively during development to cull unnecessary cells. Apop

tosis is carefully sequenced to prevent damage to surrounding cells (see

necrosis).

ASP-2: see beta-secretase.

366 G L O S S A R Y

ATP: adenosine triphosphate. The cellular "energy currency." Just as you can

use many different fuels (enriched uranium, coal, solar energy) and turn it

into useable "universal energy" (electricity) to fuel a wide range of devices

(DVD players, food processors, washing machines), so the body uses the

chemical energy stored in various fuels (glucose, amino acids, fatty acids,

etc) to make ATP to drive many of its metabolic processes.

ATPase, vacuolar: an energy- (that is, ATP-) consuming pump located on the

membrane of the lysosome that drives extra protons into the lysosome

from the main body of the cell, increasing its acidity.

B cells: cells of the immune system that recognise specific markers (antigens)

on the surfaces of invaders that mark them as foreign, and churn out anti

bodies to them. Mostly responsible for defending us against pathogens like

bacteria and parasites that are purely foreign to the body, and that can

therefore be targeted directly for destruction.

BACE: see beta-secretase.

Basement membrane: the biological filter material of the kidney.

Beta-amyloid protein (also called "amyloid beta"): a peptide formed from amy

loid precursor protein that accumulates as the waxy "senile plaques" that

cluster around the brain cells of people with Alzheimer's disease, choking

off the neurons' nourishment and preventing their normal functioning.

Beta-secretase: an enzyme with an uncertain function that sometimes mistak

enly processes Amyloid Precursor Protein, contributing to the formation of

beta-amyloid protein.

Biogerontology: The study of biological aging aimed at understanding it better.

Biological aging: the universal, progressive, and deleterious process of escalat

ing loss of molecular fidelity with age, resulting stochastically from the in

trinsic metabolic processes of the organism, that degrades its ability to

maintain homeostasis in the face of environmental stressors, leading to in

creased intrinsic vulnerability to pathology and mortality.

Biomedical gerontology: The study of biological aging aimed at combating it

in humans.

Blastocyst: the very primitive ball of cells that is formed within just a few days

after sperm meets egg. The embryo only remains in this stage of develop

ment very briefly; it has developed much further by the time the embryo is

implanted in the womb.

Blood-brain barrier: the protective layer of cells surrounding the blood vessels

that feed the brain, that denies many molecules in the circulation free ac

cess to the brain.

C. elegans: see Caenorhabditis elegans.

Caenorhabditis elegans (C. elegans): a nematode (roundworm) that is now

widely used to study genetic pathways involved in the rate of aging.

Calorie restriction (CR): Reducing the amount of food energy (calories) in

G L O S S A R Y 367

the diet while maintaining adequate levels of essential vitamins, minerals,

fats, and protein. In laboratory rodents and many other species, calorie

restriction slows down aging—extending life beyond its 'natural' limits

while preserving youthful functionality and protecting against nearly all

age-related diseases and degenerative processes—in direct proportion to

the level of restriction: fewer calories lead to more healthy, youthful life

span. The first and best-studied way to slow down aging in mammals. Also

known as "dietary restriction," "energy restriction," or "food restriction."

Calorie restriction mimetic (CR mimetic): A substance that would induce

metabolic changes that would reproduce the essential anti-aging features

of calorie restriction.

Carbonyl: an organic molecule with a carbon atom double-bonded to an oxy

gen atom. This structure makes many carbonyls highly biologically active,

and many virulent precursors of advanced glycation end products are car

bonyls such as oxoaldehydes.

Carboxymethyllysine (CML): a common advanced glycation endproduct de

rived from glycoxidation. Can also be an advanced lipoxidation endproduct.

Catalase: an enzyme produced by the body that detoxifies hydrogen peroxide

by breaking it down into water and oxygen.

CD28: a receptor on the surface of T cells that allows antigen-presenting cells to

identify the CD8 cells that target the antigen found by the APCs.

CD4 cells: cells of the immune systems that help other immune cells to ramp

up their counteroffensive when pathogens first invade. Also known as

"T-helper" cells.

CD8 cells: see cytotoxic T cells.

Cerebral amyloid angiopathy (CAA): a disease caused when beta-amyloid

binds up the interior surfaces of the brain's blood vessels, crusting them

up, weakening them, and reducing their ability to flex in response to the

surging flow of the pulse. This leaves them vulnerable to bursting open in

a bleeding stroke.

Cerebrospinal fluid (CSF): the fluids bathing the brain and spinal cord.

Ceroid: substances that share many of lipofuscin's properties (and are therefore

often confused for it) but are much easier for the cell to break down and

do not accumulate in "normal" biological aging.

Chelate: to tie up a metal in unreactive form.

Clonal expansion: the process whereby a single cell (such as a memory cyto

toxic T cell) reproduces itself in large numbers, creating a "clone" of iden

tical cells.

CML: see carboxymethyllysine.

CMV: see cytomegalovirus.

Code disparity: differences in the "languages" made from the DNA "letters" of

genes in the mitochondria and cell nucleus. Code disparity makes some of

368 G L O S S A R Y

the genes in the mitochondria unreadable by the expression machinery of the

nucleus (and vice versa).

Complex V: the mitochondrial "turbine" that uses the flow of protons to fuel

the storage of energy as ATP.

CR: see Calorie restriction.

Creatinine: a waste product of protein breakdown that healthy kidneys effi

ciently remove, and is therefore used as a blood test of kidney function.

Crescentic glomerulonephritis: a form of highly inflammatory kidney disease

named for the crescent-shaped abnormalities that are seen in biopsies of

victims' kidneys. Once it develops, crescentic glomerulonephritis leads to

very rapid loss of kidney function.

CR mimetic: see Calorie restriction mimetic.

Cross-link: a molecular "handcuff" between adjacent proteins.

Crystallin: the clear, flexible proteins that make up the structure of the lens of

the eye.

Cytochrome c oxidase: one of the pumping complexes of the electron transport

chain.

Cytokine: an inflammatory signalling molecule of the immune system.

Cytomegalovirus (CMV): a persistent virus in the herpes family.

Cytotoxic T cells: T cells responsible for rooting out cells that are native to the

body but that have now been turned against it, such as cancer cells or cells

hijacked by viruses. Also called CD8 cells because of the characteristic re

ceptor they bear.

Dauer pathway: a hibernation-like state in roundworms like C. elegans. In the

dauer pathway, a larva suspends its development for a period than can last

much longer than the entire lifetime of a nematode that follows the nor

mal, nondauer trajectory.

Deletion: mutation that involves the total removal of large stretches of DNA,

annihilating many genes at once even though it is, strictly speaking, only a

single mutation.

Dendrimer: a tiny nanotechnology structure with exquisitely complex branch

ing structures that extend outward like bushes, forming a spherical shape.

Dendrimers' branches are engineered in a way that allows us to bind a

wide range of molecules to them.

Diastolic heart failure (DHF): heart failure when the pumping chamber of the

heart can't expand sufficiently well to take in the required volume of blood.

Diastolic pressure: the second number that you get from a blood pressure cuff,

like the "80" in "110 over 80." The baseline pressure in the arteries at rest.

DNA polymerase: the enzyme responsible for making a new copy of a cell's

DNA.

EGFR and EGFRvIII: see epidermal growth factor receptor.

Electron transport chain (ETC): the series of "pumps" that use food energy in

G L O S S A R Y 369

the form of electrons provided by NADH to fill up a "reservoir" of protons

held back by the mitochondrial inner membrane (the mitochondrial "dam"),

to drive the production of energy in the form of ATP by complex V via ox

idative phosphorylation.

Electron: a charged particle in an atom. The flow of electrons is the basis for

electricity and of oxidative phosphorylation.

Embryonic stem cell: the primordial "master cells" from which our mature

cells spring. Stem cells apparently found only in embryos, that have the

ability to become any of the many different mature cells of the body. Com

pare adult stem cell.

Engineer's school of anti-aging medicine: direct intervention in the molecular

damage of aging. Leaving metabolism alone to wreak damage on our mo

lecular structures, but preventing the ensuing damage from leading to

pathology, either by cleaning up the damage (keeping it (or restoring it to)

below the threshold at which it becomes pathological), or by devising ways

of rendering the damage itself harmless.

Enzyme: a biological catalyst that facilitates a chemical reaction in the body.

Epidermal growth factor receptor (EGFR): a receptor that stimulates cell

growth. Excessive production of EGFR, or production of a mutated form

called EGFRvIII, is implicated in many cancers.

Epigenetic structures: the "scaffolding" that is anchored to the DNA in our

chromosomes. Epigenetic structures help determine which genes are

turned on in a cell and which are turned off, allowing the same overall

DNA to be used to create cells as diverse as liver, heart, and kidney cells.

Epimutation: a permanent, unprogrammed structural alteration in the "super

structure" or "scaffolding" that controls the expression of genes. Because

changes in this "scaffolding" induce changes in the regulation of gene ex

pression (turning genes on or off), epimutations are functionally the same

as mutations and are treated as such by SENS.

Expression: the process by which the "blueprints" present in genes are exe

cuted in the creation of proteins.

Fenton reaction: chemical reaction in which transition metals make preexist

ing but relatively harmless, free radicals become more virulent.

F0/F1 ATP synthase: see complex V.

Free radicals: Usually defined as an electrically neutral atom or molecule con

taining an electron that is missing its twinned "pair." This deficiency

makes free radicals unstable and highly chemically reactive. Many free rad

icals "steal" electrons from other molecules to stabilize themselves, in the

process damaging the molecule from which the electrons are "stolen" and

often turning that molecule into a free radical itself. An excess of free rad

icals in the cell can cause oxidative stress, leading to dysfunctional meta

bolic imbalances and direct damage to key structural components such as

370 G L O S S A R Y

proteins, DNA, and fatty membranes. Many substances behave like "free

radicals" and are often called free radicals but don't, strictly, meet this def

inition (e.g., reduced iron ions (Fe 2 +); equally, some molecules that strictly

are free radicals are not harmful at all.

Gamma-secretase: an enzyme required for the normal processing of Amyloid

Precursor Protein but that can also play a role in its abnormal processing

into beta-amyloid protein, particularly if the enzyme is mutated and thus

produces an abnormal form of the enzyme.

Geriatrician's school of anti-aging medicine: attempting to interfere with the

pathological consequences of aging as they come up, by treating them med-

ically on a one-by-one basis.

Gerontologists' school of anti-aging medicine: attempting to interfere with the

mechanisms of aging, by cleaning up the biochemically "messy" processes

of metabolism or by neutralizing the reactive by-products of metabolism

before they cause damage to our molecular structures.

Gerontology: the study of "aging," in any of its aspects or meanings: the psy

chology of the old in our society; the prejudices against old people; the so

cial structures that support or restrict the access of the frail elderly to

society; and the biology of aging (biogeronto logy) .

Glial cell: part of the caretaking support staff of neurons.

Glioblastoma multiforme: a rare, extremely aggressive, and hard-to-treat brain

cancer.

Glucosepane: a complex advanced glycation end-product that is the single most

important contributor to the body's AGE burden known to date, tying up

as much as one out of every five molecules of the key structural protein col

lagen in old, nondiabetic humans.

Glycated hemoglobin (HbA1c): an Amadori product that forms on red blood

cells. Because HbA1c persists for 2-3 months, it reflects average blood

sugar levels for that time period, and so is used as a lab test to measure

overall blood sugar control.

Glycation: the spontaneous chemical bonding of sugar molecules to proteins.

Glycoxidation: the accelerated conversion of some precursors of advanced gly

cation end-products into those end-products by free radicals.

HbA1c: see glycated hemoglobin.

Herceptin: a monoclonal antibody used as a targeted cancer therapy. Herceptin

targets a receptor called HER-2 that stimulates cell growth. By tying up

HER-2, herceptin prevents the excessive growth of cancer cells dependent

on overstimulation from HER-2 to keep up their very rapid rate of repro

duction.

Homeostasis: the ability of the cell or organism to maintain a defined meta

bolic equilibrium.

G L O S S A R Y 371

Hydrogen peroxide: a molecule that acts like a free radical. Produced from the

breakdown of superoxide radicals.

Hydrolase: an enzyme that breaks down a compound by combining it with wa

ter molecules. Most of the enzymes of the lysosome are hydrolases.

Innate immune system: the branch of the immune system that doesn't have to

"learn" to identify a specific enemy. Its job is similar to that of regular sol

diers on patrol in a demilitarized zone, trying to maintain order but unsure

of who might be the enemy, ready to confront anything suspicious-looking

that it happens upon.

Insulin: the hormone whose job it is to move carbohydrates and amino acids

into fat and muscle cells.

Intein: sequences that are inserted temporarily into some proteins when they

are first synthesised, possibly to help the protein mature into its final form

properly, and are then snipped out once they've served their purpose.

Isolated systolic hypertension (ISH): the kind of high blood pressure in which

a person's systolic reading (the first of the two numbers that you get from a

blood pressure cuff, like the "110" in "110 over 80") is high, even though

their diastolic pressure (the second number) is fine

K2P: a major advanced glycation endproduct in the lenses of our eyes and possi

bly other tissues.

KLRG1: a receptor that prevents cytotoxic T cells from proliferating when no

infection is present. Healthy cells bearing KLRG1 are able to reproduce

when a threat is actually present; anergic CD8 cells cannot, because of an

other receptor called CD57.

LEV: see Longevity Escape Velocity.

Lipofuscin (lip-oh-FEW-sin): a catch-all term for the mixture of stubborn

waste products that builds up in the lysosomes of long-lived cells like those

of the heart and the brain as we age. A chemical hodgepodge of fatty and

proteinaceous materials derived from membranes, reactive metals like iron

and copper, and a variety of other organic molecules that the normal com

plement of enzymes in the lysosome doesn't know how to deal with and so

refuse to be broken down after being sent there. Glows red when exposed

to light of a particular wavelength. Called popularly, "age pigment."

Longevity escape velocity (LEV): a threshold rate of biomedical progress that

will allow us to stave off aging indefinitely. The point at which each suc

cessive round of refinements to the SENS age-reversing toolkit is buying

us more time than we need to develop the next round of refinements, until

we can eventually escape age-related decline indefinitely, however old we

become in purely chronological terms.

Lysosomal storage diseases (LSDs): a range of genetic disorders caused by

failure, by one mechanism or another, of the lysosomes. Many sufferers

372 G L O S S A R Y

completely lack the gene for a lysosomal enzyme, or bear a mutated copy of

it, resulting in a misshapen and ineffective version of the protein. In other

cases, the problem is that one of the specialized transport proteins on the

surface of the lysosomal membrane is missing or defective, so that the lyso

some can't bring the junk into itself to break it down. LSDs all result in

deadly degenerative diseases, with specific symptoms varying based on

which organs a given mutation affects, and how severely.

Lysosome: An acidic organelle that uses enzymes to break damaged cellular

components down at the molecular level into more basic constituents that

can be used as raw materials for the biosynthesis of new cellular mem

branes, enzymes, and other important components of the cellular machin

ery. The biological "garbage incinerator" or "recycling center." The extra

protons that create the lysosome's acidity are actively pumped out of the

main chamber of the cell and into the lysosome by an energy- (that is,

ATP-) consuming pump located on its membrane (the vacuolar ATPase).

Maillard reaction: a major form of glycation chemistry, in which a molecule of

sugar opens its structure and glues onto a protein molecule, forming a

Schiff base. This structure is relatively unstable, so the Schiff base will of

ten spontaneously fall apart. Sometimes, however, it will collapse into a

more stable Amadori product.

Matrix metalloproteinases (MMPs): protein-digesting enzymes that act as the

"demolition teams" of tissue remodeling, clearing away the old, damaged

"scaffolding" in which cells are embedded in a tissue, making space for

new growth.

Maximum life span: see species maximum life span.

Memapsin: see beta-secretase.

Memory cytotoxic T cells: specialized to attack hijacked cells bearing antigens

encountered in previous immunological battles.

Meningoencephalitis: life-threatening swelling of the brain, apparently as a re

sult of an overreaction of the immune system inside the brain.

Metabolism: the sum of the physical and chemical processes that occur in the

living body, including the breakdown and buildup of body structures and

proteins, and the uptake, distribution within the body, chemical and phys

ical transformation, and ultimate elimination of food, air, and other com

pounds taken in from the environment.

Metastasis: the process whereby cancerous cells escape from the restraints of

the tissue in which they were originally embedded, and begin a new colony

in tissues far removed from the original cancer site.

Methylglyoxal: a major oxoaldehyde precursor of advanced glycation end prod

ucts, up to 40,000 times more reactive than blood sugar.

Microglia: the immune cells of the brain.

Mitochondria: the cellular "power plants" that take the body's raw fuels (glu-

G L O S S A R Y 373

cose, amino acids, fatty acids, etc) and turn them into useable cellular en

ergy (adenosine triphosphate—ATP).

Mitochondrial inner membrane: mitochondrial "dam" that holds back the

"reservoir" of protons used to drive the production of ATP by Complex V

(the "turbine" of the mitochondrial "hydroelectrical dam").

Mitochondriopathies: a class of diseases caused by defects in the inherited mi

tochondrial DNA (or, more rarely, by mutations acquired through causes

independent of the aging process). These mutations lead to a failure of en

ergy production that causes a spectrum of dysfunctions in various organs,

depending on the exact mutation involved.

MMPs: see matrix metalloproteinases.

Monoclonal antibody: an antibody produced on a mass scale in the laboratory

to target a specific antigen.

Monomer, beta-amyloid: an individual fragment of beta-amyloid protein that

initially floats free in the brain.

mRNA: the cell's transcripts of the DNA instructions.

Mutation: a permanent, unprogrammed structural alteration in the DNA. As

used in Chapter 12, includes epimutations.

Myelin sheath: insulating material that surrounds nerves.

Myeloperoxidase: an enzyme used by macrophages to kill bacteria by generat

ing toxic hypochlorous acid.

NAD+/NADH: A biological "carrier molecule" that shuttles electrons from

food into the mitochondria.

Naive cytotoxic T cells: a reserve of as-yet-unspecialized cytotoxic T cells that

are ready to identify new threats, "learn" about their key antigens, and

then mount an attack.

Nanotechnology: engineering performed at the molecular level.

Necrosis: traumatic, uncontrolled death of a cell. Necrosis usually causes the

cell to swell and break open, harmfully releasing its contents and damag

ing neighboring cells.

Neurite: the branching "fiber optic cables" that allow neurons to talk with one

another.

Neuron: a main type of cell of the brain and nervous system, specialized to re

ceive and transmit information from the body and from other neurons.

Neuropathy, diabetic: the debilitating damage to the nerves that is suffered

by so many diabetics, resulting from the degeneration of the insulating

myelin sheaths, complicated by the slow shrinking away of the "electric ca

bles" (dendrites and axons) through which nerves communicate with one

another.

Notch receptor 1 (NOTCH1), a protein required for the activation of stem

cells, the growth of new blood vessels, and the maturation of some kinds of

immune cells.

374 G L O S S A R Y

N-phenacylthiazolium bromide (PTB): a thiazolium breaker of advanced glyca

tion end products. Chemical cousin and predecessor of alagebrium.

Nucleus: the part of the cell that houses its central DNA genetic instructions.

Oligomer, beta-amyloid: a short chain of monomers of beta-amyloid protein

that can still float free in the brain.

Organelle: a self-contained cellular "factory" that exists outside the nucleus

and carries out specific metabolic functions for the cell as a whole. Exam

ples include mitochondria and lysosomes.

Oxidant: substances that chemically "need" electrons. Includes many free radi

cals, but also normal biochemical intermediates that are sometimes re

quired to be in this state.

Oxidating agent: see oxidant.

Oxidative phosphorylation (OXPHOS): The "charging up" of the "battery"

of ATP by complex V, achieved by adding phosphorus to its precursor mol

ecule. Consumes oxygen and produces carbon dioxide and water, and thus

called cellular respiration.

Oxidative stress: the imbalance of those substances in the body that tend to

chemically "need" electrons (oxidants including free radicals, but also nor

mal biochemical intermediates that are sometimes required to be in this

state) relative to substances that chemically "want" to donate them (reduc-

tants or reducing agents). Oxidative stress increases the risk that free radi

cals will damage key cellular components instead of being detoxified, and

can also cause dysfunctional imbalances in metabolic processes by shifting

the electrical homeostasis of the cell.

Oxoaldehyde: a highly reactive carbonyl intermediate product of glycation

chemistry.

OXPHOS: see oxidative phosphorylation.

Passive vaccination: directly providing antibodies against an antigen that we

want to target for immune attack, bringing out the immune response that

the same antibodies elicit when they are produced by the body.

Pentosidine: one of the more easily measured advanced glycation end products.

Pimagidine: see aminoguanidine.

Point mutations: mutations that change only one, or a few, of the "letters" in one

"word" in the "sentence" of instructions comprising an individual gene.

Prodrug: a substances that is inactive until metabolized in some way, where

upon it is chemically transformed into a pharmacologically active product.

Proton: an electrically charged particle present in the atom. The flow of pro

tons across the mitochondrial inner membrane through complex V provides

the power to drive the storage of cellular energy as ATP.

Receptor: a molecular "lock" on the surface of the cell that responds to the

correct molecular "key" by performing functions like opening the cell up

to a needed nutrient or inducing a signaling cascade.

G L O S S A R Y 375

Reductant: a substance that characteristically "wants" to give electrons to

other compounds.

Retinopathy, diabetic: vision loss in diabetics linked to damage to the fine

blood vessels feeding the light-absorbing tissues at the back of the eyeball.

RMR: see robust mouse rejuvenation.

Robust mouse rejuvenation (RMR): the irrefutable reversal of aging in mice.

RMR will be achieved when we can take at least twenty mice of the

species Mus musculus (the common house or laboratory mouse), of a

healthy strain (one with a normal average life span of at least three years),

and administer anti-aging treatments starting only when they are at least

two years old that lead them to be able to live in good health to an average

of five years.

SA-beta-gal: see Senescence-associated beta-galactosidase.

Schiff base: a compound that can result from various glycation reactions that

contains a double bond between carbon and nitrogen atom, with specific

classes of compounds connected to it in turn through the nitrogen atom.

The Schiff bases that result from glycation are unstable and tend to go on

to form Amadori products.

SCNT: see somatic cell nuclear transfer.

Senescence-associated beta-galactosidase (SA-beta-gal): an enzyme whose ac

tivity identifies senescent cells.

Senescent cells: cells that have lost the ability to divide as a result of aging dam

age (and, usually, the body's response to that damage).

SENS: Strategies for Engineered Negligible Senescence. The scientific plat

form for anti-aging medicine based on the heuristic of the engineer's school

of anti-aging medicine.

Serotonin: a chemical messenger in neurons (and elsewhere) involved in mood,

appetite, thought, and sensory perception. Serotonin is the substance whose

metabolism is modulated by drugs like Prozac.

Somatic cell nuclear transfer (SCNT): The process of making new, perfectly-

matched embryonic stem cells out of a specialized mature cell (a "somatic

cell") from a patient by fusing it with an egg cell, provided by a prospec

tive stem cell recipient, whose cell nucleus is removed to make way for

the one from the patient's cell. When the fused cell begins dividing, it

creates ESCs with the donor's genetic code, and so with absolutely no

risk of rejection.

Species maximum life span: how long the oldest old of the species (and not just

of a particular strain of them, or of the cohort of animals in which the in

tervention was tested) can live under the best possible conditions.

Stem cell: an early, unspecialized cell that can renew itself indefinitely and de

velop into one or more of the highly specialized, mature cells of each tissue

in the body. Includes embryonic stem cells and adult stem cells.

376 G L O S S A R Y

Subcutaneous fat: the fat that lies under your skin all over the body, producing

a "pear shape" when present in excess. Compare visceral fat.

Superoxide radical: a free radical produced by the "fumbling" of electrons by

the electron transport chain in the mitochondria.

Systemic AL amyloidosis: the most common form of amyloidosis in the United

States and some other industrialised countries, caused by overproduction by

a kind of blood cell of a component of a class of antibodies called "im

munoglobulin light chain" (L—thus "AL," for "Amyloidosis Light-chain").

Systolic blood pressure: the first of the two numbers that you get from a blood

pressure cuff, like the "110" in "110 over 80." A measure of how much

pressure is applied to the artery wall by the surge of blood into the vessel

as the heart contracts.

T cells: immune cells that mature in the thymus. Includes cytotoxic T cells and

helper T cells.

Targeted cancer therapy: a selective cancer treatment that "targets" cancer

cells selectively. Usually refers specifically to drugs that interfere with spe

cific receptors or signaling processes upon which a particular cancer relies

strongly.

Targeting sequence: a special string of amino acids that when appended to the

"nose" of a protein produced in the main body of the cell, directs it into a

particular location such as the mitochondria.

Telomerase: the enzyme that relengthens shortened telomeres.

Telomeres: long stretches of DNA present at the ends of all our chromosomes

that contain no protein blueprints. Telomeres are worn down with each

round of DNA replication.

T-helper cells: see CD4 cells.

Therapeutic cloning: see somatic cell nuclear transfer.

Thiazolium: member of a class of compounds with a chemical structure related

to thiamin (vitamin B1).

Thymidine kinase (TK): an enzyme that is required for the synthesis of DNA.

TIM/TOM complex: short for "Translocase of the Inner Mitochondrial mem

brane" (TIM) and the "Translocase of the Outer Mitochondrial membrane"

(TOM). The elaborate machinery that specifically moves ("translocates")

proteins through the mitochondrial membranes.

TK: see thymidine kinase.

Transition metals: elements like iron and copper that can intensify oxidative

stress through their role in the Fenton reaction.

Translocase of the Inner Mitochondrial membrane (TIM): see TIM/TOM

Complex.

Translocase of the Outer Mitochondrial membrane (TOM): see TIM/TOM

Complex.

Triglycerides: fats; especially fats circulating in the blood.

G L O S S A R Y 377

Vacuolar ATPase: see ATPase, vacuolar.

Vascular endothelial growth factor (VEGF): a chemical messenger that stimu

lates new blood vessel growth.

VEGF: see vascular endothelial growth factor.

Visceral fat: fat tissue that surrounds your internal organs, as opposed to the

subcutaneous fat that lies under your skin all over the body. Too much vis

ceral fat is responsible for an "apple-shaped" or "beer-bellied" overweight

appearance. Visceral fat appears to be implicated in much of the metabolic

derangement of diabetes and of aging.

Aubrey de Grey - Ending Aging

Documents

Transcript of Aubrey de Grey - Ending Aging